While infection with rubella during pregnancy causes fewer than 1% of cases of autism, vaccination against rubella can prevent many of those cases.

There is no known cure. Children recover occasionally, so that they lose their diagnosis of ASD; this occurs sometimes after intensive treatment and sometimes not. It is not known how often recovery happens; reported rates in unselected samples of children with ASD have ranged from 3% to 25%. Most children with autism acquire language by age five or younger, though a few have developed communication skills in later years. Most children with autism lack social support, meaningful relationships, future employment opportunities or self-determination. Although core difficulties tend to persist, symptoms often become less severe with age.

Few high-quality studies address long-term prognosis. Some adults show modest improvement in communication skills, but a few decline; no study has focused on autism after midlife. Acquiring language before age six, having an IQ above 50, and having a marketable skill all predict better outcomes; independent living is unlikely with severe autism. Most people with autism face significant obstacles in transitioning to adulthood.

There is some evidence that children with AS may see a lessening of symptoms; up to 20% of children may no longer meet the diagnostic criteria as adults, although social and communication difficulties may persist. As of 2006, no studies addressing the long-term outcome of individuals with Asperger syndrome are available and there are no systematic long-term follow-up studies of children with AS. Individuals with AS appear to have normal life expectancy, but have an increased prevalence of comorbid psychiatric conditions, such as major depressive disorder and anxiety disorder that may significantly affect prognosis. Although social impairment may be lifelong, the outcome is generally more positive than with individuals with lower functioning autism spectrum disorders; for example, ASD symptoms are more likely to diminish with time in children with AS or HFA. Most students with AS/HFA have average mathematical ability and test slightly worse in mathematics than in general intelligence, but some are gifted in mathematics. AS has potentially been linked to some accomplishments, such as Vernon L. Smith winning the Nobel Memorial Prize in Economic Sciences; however, Smith is self-diagnosed.

Although many attend regular education classes, some children with AS may utilize special education services because of their social and behavioral difficulties. Adolescents with AS may exhibit ongoing difficulty with self care or organization, and disturbances in social and romantic relationships. Despite high cognitive potential, most young adults with AS remain at home, yet some do marry and work independently. The "different-ness" adolescents experience can be traumatic. Anxiety may stem from preoccupation over possible violations of routines and rituals, from being placed in a situation without a clear schedule or expectations, or from concern with failing in social encounters; the resulting stress may manifest as inattention, withdrawal, reliance on obsessions, hyperactivity, or aggressive or oppositional behavior. Depression is often the result of chronic frustration from repeated failure to engage others socially, and mood disorders requiring treatment may develop. Clinical experience suggests the rate of suicide may be higher among those with AS, but this has not been confirmed by systematic empirical studies.

Education of families is critical in developing strategies for understanding strengths and weaknesses; helping the family to cope improves outcomes in children. Prognosis may be improved by diagnosis at a younger age that allows for early interventions, while interventions in adulthood are valuable but less beneficial. There are legal implications for individuals with AS as they run the risk of exploitation by others and may be unable to comprehend the societal implications of their actions.

Frequency estimates vary enormously. In 2015 it was estimated that 37.2 million people globally are affected. A 2003 review of epidemiological studies of children found autism rates ranging from 0.03 to 4.84 per 1,000, with the ratio of autism to Asperger syndrome ranging from 1.5:1 to 16:1; combining the geometric mean ratio of 5:1 with a conservative prevalence estimate for autism of 1.3 per 1,000 suggests indirectly that the prevalence of AS might be around 0.26 per 1,000. Part of the variance in estimates arises from differences in diagnostic criteria. For example, a relatively small 2007 study of 5,484 eight-year-old children in Finland found 2.9 children per 1,000 met the ICD-10 criteria for an AS diagnosis, 2.7 per 1,000 for Gillberg and Gillberg criteria, 2.5 for DSM-IV, 1.6 for Szatmari "et al.", and 4.3 per 1,000 for the union of the four criteria. Boys seem to be more likely to have AS than girls; estimates of the sex ratio range from 1.6:1 to 4:1, using the Gillberg and Gillberg criteria. Females with autism spectrum disorders may be underdiagnosed.

Anxiety disorder and major depressive disorder are the most common conditions seen at the same time; comorbidity of these in persons with AS is estimated at 65%. Reports have associated AS with medical conditions such as aminoaciduria and ligamentous laxity, but these have been case reports or small studies and no factors have been associated with AS across studies. One study of males with AS found an increased rate of epilepsy and a high rate (51%) of nonverbal learning disorder. AS is associated with tics, Tourette syndrome, and bipolar disorder, and the repetitive behaviors of AS have many similarities with the symptoms of obsessive–compulsive disorder and obsessive–compulsive personality disorder. However many of these studies are based on clinical samples or lack standardized measures; nonetheless, comorbid conditions are relatively common.

Although little is known about the biological basis of autism, studies have revealed structural abnormalities in specific brain regions. Regions identified in the "social" brain include the amygdala, superior temporal sulcus, fusiform gyrus area and orbitofrontal cortex. Further abnormalities have been observed in the caudate nucleus, believed to be involved in restrictive behaviors, as well as in a significant increase in the amount of cortical grey matter and atypical connectivity between brain regions.

There is a mistaken belief that some vaccinations, such as the MMR, the measles/mumps vaccine, may cause autism. This was based on a research study published by Andrew Wakefield, which has been determined fraudulent and retracted. The results of this study caused some parents to take their children off the vaccines; these diseases can cause intellectual disabilities or death. The claim that some vaccinations cause autism has not been proven through multiple large-scale studies conducted in Japan, the United States, and other countries.

High-functioning autism is characterized by features very similar to those of Asperger syndrome. The defining characteristic most widely recognized by psychologists is a significant delay in the development of early speech and language skills, before the age of three years. The diagnostic criteria of Asperger syndrome exclude a general language delay.

Further differences in features between people with high-functioning autism and those with Asperger syndrome, include the following:

- People with HFA have a lower verbal reasoning ability

- Better visual/spatial skills (higher performance IQ) than people with Asperger syndrome

- Less deviating locomotion than people with Asperger syndrome

- People with HFA more often have problems functioning independently

- Curiosity and interest for many different things, in contrast to people with Asperger syndrome

- People with Asperger syndrome are better at empathizing with another

- The male to female ratio of 4:1 for HFA is much smaller than that of Asperger syndrome

Individuals with autism spectrum disorders, including high-functioning autism, risk developing symptoms of anxiety. While anxiety is one of the most commonly occurring mental health symptoms, children and adolescents with high functioning autism are at an even greater risk of developing symptoms.

There are other comorbidities, the presence of one or more disorders in addition to the primary disorder, associated with high-functioning autism. Some of these include depression, bipolar disorder, and obsessive compulsive disorder (OCD). In particular the link between HFA and OCD, has been studied; both have abnormalities associated with serotonin.

Observable comorbidities associated with HFA include ADHD, Tourette syndrome, and possibly criminal behavior. While the association between HFA and criminal behavior is not completely characterized, several studies have shown that the features associated with HFA may increase the probability of engaging in criminal behavior. While there is still a great deal of research that needs to be done in this area, recent studies on the correlation between HFA and criminal actions suggest that there is a need to understand the attributes of HFA that may lead to violent behavior. There have been several case studies that link the lack of empathy and social naïveté associated with HFA to criminal actions.

HFA does not cause nor include intellectual disabilities. This characteristic distinguishes HFA from the rest of the autism spectrum; between 40 and 55% of individuals with autism also have an intellectual disability.

A high-functioning alcoholic (HFA) is a person who maintains jobs and relationships while exhibiting alcoholism.

Statistics from the Harvard School of Public Health indicated that 31 percent of college students show signs of alcohol abuse and 6 percent are dependent on alcohol. Doctors hope that the new definition will help identify severe cases of alcoholism early, rather than when the problem is fully developed.

Many HFAs are not viewed as alcoholics by society because they do not fit the common alcoholic stereotype. Unlike the stereotypical alcoholic, HFAs have either succeeded or over-achieved throughout their lifetimes. This can lead to denial of alcoholism by the HFA, co-workers, family members, and friends. Functional alcoholics account for 19.5 percent of total U.S. alcoholics, with 50 percent also being smokers and 33 percent having a multigenerational family history of alcoholism.