The PCL-R, the PCL:SV, and the PCL:YV are highly regarded and widely used in criminal justice settings, particularly in North America. They may be used for risk assessment and for assessing treatment potential and be used as part of the decisions regarding bail, sentence, which prison to use, parole, and regarding whether a youth should be tried as a juvenile or as an adult. There have been several criticisms against its use in legal settings. They include the general criticisms against the PCL-R, the availability of other risk assessment tools which may have advantages, and the excessive pessimism surrounding the prognosis and treatment possibilities of those who are diagnosed with psychopathy.

The interrater reliability of the PCL-R can be high when used carefully in research but tend to be poor in applied settings. In particular Factor 1 items are somewhat subjective. In sexually violent predator cases the PCL-R scores given by prosecution experts were consistently higher than those given by defense experts in one study. The scoring may also be influenced by other differences between raters. In one study it was estimated that of the PCL-R variance, about 45% was due to true offender differences, 20% was due to which side the rater testified for, and 30% was due to other rater differences.

To aid a criminal investigation, certain interrogation approaches may be used to exploit and leverage the personality traits of suspects thought to have psychopathy and make them more likely to divulge information.

The prognosis for psychopathy in forensic and clinical settings is quite poor, with some studies reporting that treatment may worsen the antisocial aspects of psychopathy as measured by recidivism rates, though it is noted that one of the frequently cited studies finding increased criminal recidivism after treatment, a 2011 retrospective study of a treatment program in the 1960s, had several serious methodological problems and likely would not be approved of today. However, some relatively rigorous quasi-experimental studies using more modern treatment methods have found improvements regarding reducing future violent and other criminal behavior, regardless of PCL-R scores, although none were randomized controlled trials. Various other studies have found improvements in risk factors for crime such as substance abuse. No study has of yet in a 2013 review examined if the personality traits that form the core character disturbances of psychopathy could be changed by such treatments.

Perhaps due to their perceived rarity, the dissociative disorders (including DID) were not initially included in the Structured Clinical Interview for DSM-IV (SCID), which is designed to make psychiatric diagnoses more rigorous and reliable. Instead, shortly after the publication of the initial SCID a freestanding protocol for dissociative disorders (SCID-D) was published. This interview takes about 30 to 90 minutes depending on the subject's experiences. An alternative diagnostic instrument, the Dissociative Disorders Interview Schedule, also exists but the SCID-D is generally considered superior. The Dissociative Disorders Interview Schedule (DDIS) is a highly structured interview that discriminates among various DSM-IV diagnoses. The DDIS can usually be administered in 30–45 minutes.

Other questionnaires include the Dissociative Experiences Scale (DES), Perceptual Alterations Scale, Questionnaire on Experiences of Dissociation, Dissociation Questionnaire, and the Mini-SCIDD. All are strongly intercorrelated and except the Mini-SCIDD, all incorporate absorption, a normal part of personality involving narrowing or broadening of attention. The DES is a simple, quick, and validated questionnaire that has been widely used to screen for dissociative symptoms, with variations for children and adolescents. Tests such as the DES provide a quick method of screening subjects so that the more time-consuming structured clinical interview can be used in the group with high DES scores. Depending on where the cutoff is set, people who would subsequently be diagnosed can be missed. An early recommended cutoff was 15-20. The reliability of the DES in non-clinical samples has been questioned.

The World Health Organization's (WHO) "International Statistical Classification of Diseases and Related Health Problems", 10th Edition (ICD-10) lists narcissistic personality disorder under "Other specific personality disorders". It is a requirement of ICD-10 that a diagnosis of any specific personality disorder also satisfies a set of general personality disorder criteria.

The fourth, revised edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) diagnoses DID according to the diagnostic criteria found in section 300.14 (dissociative disorders). It has also been found difficult to diagnose the disorder in the first place, due to there not being a universal agreement of the definition of dissociation. The criteria require that an adult be recurrently controlled by two or more discrete identities or personality states, accompanied by memory lapses for important information that is not caused by alcohol, drugs or medications and other medical conditions such as complex partial seizures. While otherwise similar, the diagnostic criteria for children also specifies symptoms must not be confused with imaginative play. Diagnosis is normally performed by a clinically trained mental health professional such as a psychiatrist or psychologist through clinical evaluation, interviews with family and friends, and consideration of other ancillary material. Specially designed interviews (such as the SCID-D) and personality assessment tools may be used in the evaluation as well. Since most of the symptoms depend on self-report and are not concrete and observable, there is a degree of subjectivity in making the diagnosis. People are often disinclined to seek treatment, especially since their symptoms may not be taken seriously; thus dissociative disorders have been referred to as "diseases of hiddenness".

The diagnosis has been criticized by supporters of therapy as a cause or the sociocognitive hypothesis as they believe it is a culture-bound and often health care induced condition. The social cues involved in diagnosis may be instrumental in shaping patient behavior or attribution, such that symptoms within one context may be linked to DID, while in another time or place the diagnosis could have been something other than DID. Other researchers disagree and argue that the existence of the condition and its inclusion in the DSM is supported by multiple lines of reliable evidence, with diagnostic criteria allowing it to be clearly discriminated from conditions it is often mistaken for (schizophrenia, borderline personality disorder, and seizure disorder). That a large proportion of cases are diagnosed by specific health care providers, and that symptoms have been created in nonclinical research subjects given appropriate cueing has been suggested as evidence that a small number of clinicians who specialize in DID are responsible for the creation of alters through therapy.

ASPD commonly coexists with the following conditions:

When combined with alcoholism, people may show frontal function deficits on neuropsychological tests greater than those associated with each condition.

Sadomasochism is the giving or receiving pleasure from acts involving the receipt or infliction of pain or humiliation. Practitioners of sadomasochism may seek sexual gratification from their acts. While the terms sadist and masochist refer respectively to one who enjoys giving or receiving pain, practitioners of sadomasochism may switch between activity and passivity.

The abbreviation S&M is often used for sadomasochism, although practitioners themselves normally remove the ampersand and use the acronym S-M or SM or S/M when written throughout the literature. Sadomasochism is not considered a clinical paraphilia unless such practices lead to clinically significant distress or impairment for a diagnosis. Similarly, sexual sadism within the context of mutual consent, generally known under the heading BDSM, is distinguished from non-consensual acts of sexual violence or aggression.

The formulation of narcissistic personality disorder in the American Psychiatric Association's (APA) "Diagnostic and Statistical Manual of Mental Disorders", 4th Edition, Text Revision (DSM-IV-TR) was criticised for failing to describe the range and complexity of the disorder. Critics said it focuses overly on "the narcissistic individual's external, symptomatic, or social interpersonal patterns—at the expense of ... internal complexity and individual suffering," which they argued reduced its clinical utility.

The Personality and Personality Disorders Work Group originally proposed the elimination of NPD as a distinct disorder in DSM-5 as part of a major revamping of the diagnostic criteria for personality disorders, replacing a categorical with a dimensional approach based on the severity of dysfunctional personality trait domains. Some clinicians objected to this, characterizing the new diagnostic system as an "unwieldy conglomeration of disparate models that cannot happily coexist" and may have limited usefulness in clinical practice. The general move towards a dimensional (personality trait-based) view of the Personality Disorders has been maintained despite the reintroduction of NPD.

Sexual sadism disorder is the condition of experiencing sexual arousal in response to the extreme pain, suffering or humiliation of others. Several other terms have been used to describe the condition, and the condition may overlap with other conditions that involve inflicting pain. It is distinct from situations in which consenting individuals use mild or simulated pain or humiliation for sexual excitement. The words "sadism" and "" are derived from Marquis de Sade.

With paraphilic coercive disorder, the individual employs enough force to subdue a victim, but with sexual sadism disorder, the individual often continues to inflict harm regardless of the compliance of the victim, which sometimes escalates not only to the death of the victim, but also to the mutilation of the body. What is experienced by the sadist as sexual does not always appear obviously sexual to non-sadists: Sadistic rapes do not necessarily include penile penetration of the victim. In a survey of offenses, 77% of cases included sexual bondage, 73% included anal rape, 60% included blunt force trauma, 57% included vaginal rape, and 40% included penetration of the victim by a foreign object. Moreover, in 40% of cases, the offender kept a personal item of the victim as a souvenir.

On personality testing, sadistic rapists apprehended by law enforcement have shown elevated traits of impulsivity, hypersexuality, callousness, and psychopathy.

Although there appears to be a continuum of severity from mild ("hyperdominance" or "BDSM") to moderate ("paraphilic coercive disorder") to severe ('sexual sadism disorder), it is not clear if they are genuinely related or only appear related superficially.

Very little is known about how sexual sadism disorder develops. Most of the people diagnosed with sexual sadism disorder come to the attention of authorities by committing sexually motivated crimes. Surveys have also been conducted including people who are interested in only mild and consensual forms of sexual pain/humiliation (BDSM).

Most of the people with full-blown sexual sadism disorder are male, whereas the sex ratio of people interested in BDSM is closer to 2:1 male-to-female.

People with sexual sadism disorder" are at an elevated likelihood of having other paraphilic sexual interests.

According to Professor Emily Simonoff of the Institute of Psychiatry, Psychology and Neuroscience, "childhood hyperactivity and conduct disorder showed equally strong prediction of antisocial personality disorder (ASPD) and criminality in early and mid-adult life. Lower IQ and reading problems were most prominent in their relationships with childhood and adolescent antisocial behaviour."

Erotophobia is a term coined by a number of researchers in the late 1970s and early 1980s to describe one pole on a continuum of attitudes and beliefs about sexuality. The model of the continuum is a basic polarized line, with erotophobia (fear of sex or negative attitudes about sex) at one end and erotophilia (positive feelings or attitudes about sex) at the other end.

The word erotophobia is derived from the name of Eros, the Greek god of erotic love, and Phobos, Greek (φόβος) for "fear".

Theodore Millon has proposed four subtypes of masochist. Any individual masochist may fit into none, one or more of the following subtypes:

The person's appearance, behavior, and history, along with a psychological evaluation, are usually sufficient to establish a diagnosis. There is no test to confirm this diagnosis. Because the criteria are subjective, some people may be wrongly diagnosed.

Historically, masochism has been associated with feminine submissiveness. This disorder became politically controversial when associated with domestic violence which was considered to be mostly caused by males. However a number of studies suggest that the disorder is common. In spite of its exclusion from DSM-IV in 1994, it continues to enjoy widespread currency amongst clinicians as a construct that explains a great many facets of human behaviour.

Sexual masochism that "causes clinically significant distress or impairment in social, occupational, or other important areas of functioning" is still in DSM-IV.

Obsessive love is a condition in which one person feels an overwhelming obsessive desire to possess and protect another person toward whom one feels a strong attraction, with an inability to accept failure or rejection. Although not categorized specifically under any specific mental diagnosis by the DSM-5, some people argue that obsessive love is considered to be a mental illness similar to attachment disorder, borderline personality disorder, and erotomania. Depending on the intensity of their attraction, obsessive lovers may feel entirely unable to restrain themselves from extreme behaviors such as acts of violence toward themselves or others. Obsessive love can have its roots in childhood trauma, and may begin at first sight; it may persist indefinitely, sometimes requiring psychotherapy.

Obsessive love occurs in both women and men, making it a gender neutral phenomenon.

Psychiatrists seek to provide a medical diagnosis of individuals by an assessment of symptoms, signs and impairment associated with particular types of mental disorder. Other mental health professionals, such as clinical psychologists, may or may not apply the same diagnostic categories to their clinical formulation of a client's difficulties and circumstances. The majority of mental health problems are, at least initially, assessed and treated by family physicians (in the UK general practitioners) during consultations, who may refer a patient on for more specialist diagnosis in acute or chronic cases.

Routine diagnostic practice in mental health services typically involves an interview known as a mental status examination, where evaluations are made of appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of other professionals, relatives or other third parties may be taken into account. A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in rare specialist cases neuroimaging tests may be requested, but such methods are more commonly found in research studies than routine clinical practice.

Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations. It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice. In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries.

More structured approaches are being increasingly used to measure levels of mental illness.

- HoNOS is the most widely used measure in English mental health services, being used by at least 61 trusts. In HoNOS a score of 0–4 is given for each of 12 factors, based on functional living capacity. Research has been supportive of HoNOS, although some questions have been asked about whether it provides adequate coverage of the range and complexity of mental illness problems, and whether the fact that often only 3 of the 12 scales vary over time gives enough subtlety to accurately measure outcomes of treatment.

Sadism involves gaining pleasure through themselves or others undergoing discomfort or pain. The opponent-process theory explains the way in which individuals not only display, but also enjoy committing sadistic acts. Individuals possessing sadistic personalities tend to display recurrent aggression and cruel behavior. Sadism can also include the use of emotional cruelty, purposefully manipulating others through the use of fear, and a preoccupation with violence.

Theodore Millon claimed there were four subtypes of sadism, which he termed Enforcing sadism, Explosive sadism, Spineless sadism, and Tyrannical sadism.

Sadistic personality disorder is a personality disorder involving which appeared in an appendix of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-III-R). The later versions of the DSM (DSM-IV, DSM-IV-TR and DSM-5) do not include it.

The words "sadism" and "sadist" are derived from Marquis de Sade.

Since the 1980s, Paula Caplan has been concerned about the subjectivity of psychiatric diagnosis, and people being arbitrarily “slapped with a psychiatric label.” Caplan says because psychiatric diagnosis is unregulated, doctors are not required to spend much time interviewing patients or to seek a second opinion. The Diagnostic and Statistical Manual of Mental Disorders can lead a psychiatrist to focus on narrow checklists of symptoms, with little consideration of what is actually causing the patient’s problems. So, according to Caplan, getting a psychiatric diagnosis and label often stands in the way of recovery.

In 2013, psychiatrist Allen Frances wrote a paper entitled "The New Crisis of Confidence in Psychiatric Diagnosis", which said that "psychiatric diagnosis… still relies exclusively on fallible subjective judgments rather than objective biological tests." Frances was also concerned about "unpredictable overdiagnosis." For many years, marginalized psychiatrists (such as Peter Breggin, Thomas Szasz) and outside critics (such as Stuart A. Kirk) have "been accusing psychiatry of engaging in the systematic medicalization of normality." More recently these concerns have come from insiders who have worked for and promoted the American Psychiatric Association (e.g., Robert Spitzer, Allen Frances). A 2002 editorial in the "British Medical Journal" warned of inappropriate medicalization leading to disease mongering, where the boundaries of the definition of illnesses are expanded to include personal problems as medical problems or risks of diseases are emphasized to broaden the market for medications.

Erotophobia has many manifestations. An individual or culture can have one or multiple erotophobic attitudes. Some types of erotophobia include fear of nudity, fear of sexual images, homophobia, fear of sex education, fear of sexual discourse.

Psychiatrist Kantor suggests a treatment approach using psychodynamic, supportive, cognitive, behavioral and interpersonal therapeutic methods. These methods apply to both the Passive–aggressive person and their target victim.

SPD can be first apparent in childhood and adolescence with solitariness, poor peer relationships, and underachievement in school. This may mark these children as different and make them subject to teasing.

Being a personality disorder, which are usually chronic and long-lasting mental conditions, schizoid personality disorder is not expected to improve with time without treatment; however, much remains unknown because it is rarely encountered in clinical settings.

The previous edition of the Diagnostic and Statistical Manual of Mental Disorders, DSM IV-TR, defines histrionic personality disorder (in Cluster B) as:

The DSM-IV requires that a diagnosis for any specific personality disorder also satisfies a set of general personality disorder criteria.

Malignant narcissism is a psychological syndrome comprising an extreme mix of narcissism, antisocial behavior, aggression, and sadism. Often grandiose, and always ready to raise hostility levels, the malignant narcissist undermines organizations in which they are involved, and dehumanizes the people with whom they associate.

Malignant narcissism is a hypothetical, experimental diagnostic category. Narcissistic personality disorder is found in the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-IV-TR), while malignant narcissism is not. As a hypothetical syndrome, malignant narcissism could include aspects of narcissistic personality disorder as well as paranoia. The importance of malignant narcissism and of projection as a defense mechanism has been confirmed in paranoia, as well as "the patient's vulnerability to malignant narcissistic regression".