Most girls can stay dry at night by age six and most boys stay dry by age seven. Boys are three times more likely to wet the bed than girls.

Doctors frequently consider bedwetting as a self-limiting problem, since most children will outgrow it. Children 5 to 9 years old have a spontaneous cure rate of 14% per year. Adolescents 10 to 18 years old have a spontaneous cure rate of 16% per year.

Approximate bedwetting rates are:

- Age 5: 20%

- Age 6: 10–15%

- Age 7: 7%

- Age 10: 5%

- Age 15: 1–2%

- Age 18–64: 0.5–1%

As can be seen from the numbers above, a portion of bedwetting children will not outgrow the problem. Adult rates of bedwetting show little change due to spontaneous cure. Persons who are still enuretic at age 18 are likely to deal with bedwetting throughout their lives.

Studies of bedwetting in adults have found varying rates. The most quoted study in this area was done in the Netherlands. It found a 0.5% rate for 18- to 64-year-olds. A Hong Kong study, however, found a much higher rate. The Hong Kong researchers found a bedwetting rate of 2.3% in 16- to 40-year-olds.

The aetiology of NE is not fully understood, although there are three common causes: excessive urine volume, poor sleep arousal, and bladder contractions. Differentiation of cause is mainly based on patient history and fluid charts completed by the parent or carer to inform management options.

The following list summarizes bedwetting's known causes and risk factors. Enuretic patients frequently have more than one cause or risk factor from the items listed below.

Most cases of bedwetting are PNE-type, which has two related most common causes

- Neurological-developmental delay This is the most common cause of bedwetting. Most bedwetting children are simply delayed in developing the ability to stay dry and have no other developmental issues. Studies suggest that bedwetting may be due to a nervous system that is slow to process the feeling of a full bladder.

- Genetics Bedwetting has a strong genetic component. Children whose parents were not enuretic have only a 15% incidence of bedwetting. When one or both parents were bedwetters, the rates jump to 44% and 77% respectively. Genetic research shows that bedwetting is associated with the genes on chromosomes 13q and 12q (possibly 5 and 22 also).

These first two items are the most common factors in bedwetting, but current medical technology offers no easy testing for either cause. There is no test to prove that bedwetting is only a developmental delay, and genetic testing offers little or no benefit.

As a result, other conditions should be ruled out. The following causes are less common, but are easier to prove and more clearly treated:

- Alcohol consumption Drinking alcohol increases urine production, inhibits anti-diuretic hormone production, decreases awareness, increases drowsiness and causes impulsive decisions.

- Anti-diuretic hormone (ADH) Anti-diuretic hormone regulates urine production by increasing water reabsorption in the kidney. Both insufficient production of ADH, or insufficient response to ADH, leads to an overproduction of urine, often beyond the capacity of a child's bladder. The body normally increases ADH levels at night, signalling the kidneys to produce less urine. The diurnal change may not be seen until about age 10. In some bed wetting children this increase in ADH production does not occur, while other children may produce an increased amount of ADH but their response is insufficient.

- Attention deficit hyperactivity disorder (ADHD) Children with ADHD are 2.7 times more likely to have bedwetting issues.

- Caffeine Caffeine increases urine production.

- Constipation Chronic constipation can cause bed wetting. When the bowels are full, it can put pressure on the bladder. Often such children defecate normally, yet they retain a significant mass of material in the bowel which causes bed wetting.

- Infection/disease Infections and disease are more strongly connected with and with daytime wetting. Less than 5% of all bedwetting cases are caused by infection or disease, the most common of which is a urinary tract infection.

- More severe neurological-developmental issues Patients with intellectual disabilities have a higher rate of bedwetting problems. One study of seven-year-olds showed that "handicapped and intellectually disabled children" had a bedwetting rate almost three times higher than "non-handicapped children" (26.6% vs. 9.5%, respectively).

- Physical abnormalities Less than 10% of enuretics have urinary tract abnormalities, such as a smaller than normal bladder. Current data does support increased bladder tone in some enuretics, which functionally would decrease bladder capacity.

- Psychological Psychological issues (e.g., death in the family, sexual abuse, extreme bullying) are established as a cause of (a return to bedwetting), but are very rarely a cause of PNE-type bedwetting. Bedwetting can also be a symptom of a pediatric neuropsychological disorder called PANDAS. When enuresis is caused by a psychological or neuropsychological disorder, the bedwetting is considered a "symptom" of the disorder. Enuresis has a psychological diagnosis code (see previous section), but it is not considered a psychological condition itself. (See section on psychological/social impact, below)

- Sleep apnea Sleep apnea stemming from an upper airway obstruction has been associated with bedwetting. Snoring and enlarged tonsils or adenoids are a sign of potential sleep apnea problems.

- Sleepwalking Sleepwalking can lead to bedwetting. During sleepwalking, the sleepwalker may think he/she is in another room. When the sleepwalker urinates during a sleepwalking episode, he/she usually thinks they are in the bathroom, and therefore urinate where they think the toilet should be. Cases of this have included opening a closet and urinating in it; urinating on the sofa and simply urinating in the middle of the room.

- Stress Stress is not a cause of "primary" nocturnal enuresis (PNE), but is well established as a cause of returning to bedwetting (). Researchers studying children who have yet to stay dry find "no relationship to social background, life stresses, family constellation, or number of residencies." On the other hand, stress is a cause of people who return to wetting the bed. Researchers find that moving to a new town, parent conflict or divorce, arrival of a new baby, or loss of a loved one or pet can cause insecurity, contributing to returning bedwetting.

- Type 1 Diabetes Mellitus Nocturnal enuresis could be the presenting symptom of type 1 diabetes mellitus, classically associated with polyuria, polydipsia, and polyphagia; weight loss, lethargy, and diaper candidiasis may also be present in those with new-onset disease.

Certain inherited genes appear to contribute to incontinence. In 1995, Danish researchers announced they had found a site on human chromosome 13 that is responsible, at least in part, for nighttime wetting. If both parents were enuretic, 77% of their children are too; if only one parent was enuretic, then 44% of their offspring are also. Experts believe that other, undetermined genes also may be involved in incontinence.

Experts suggest that anxiety-causing events occurring in the lives of children ages 2 to 4 might lead to incontinence before the child achieves total bladder control. Anxiety experienced after age 4 might lead to wetting after the child has been dry for a period of 6 months or more. Such events include angry parents, unfamiliar social situations, and overwhelming family events such as the birth of a brother or sister.

Incontinence itself is an anxiety-causing event. Strong bladder contractions leading to leakage in the daytime can cause embarrassment and anxiety that lead to wetting at night.

Daytime wetting is more common in girls than in boys, but bedwetting is three times as prevalent in boys (i.e., around 75% of sufferers are male). At the age of 7 approximately 3% of girls and 2% of boys experience functional daytime wetting at least once a week.

Common causes include, but not limited to:

- Incomplete emptying of the bladder

- Irritable bladder

- Constipation

- Stress

- Urinary tract infection

- Urgency (not “making it” to the bathroom in time)

- Anatomic abnormality

- Poor toileting habits

- Small bladder capacity

- Medical conditions like overactive bladder disorder

According to one meta-analysis, the mean prevalence rate for North America and Western Europe is estimated to be 14.5±8.0%. Specifically in the United States, the prevalence of restless leg syndrome is estimated to be between 5 and 15.7% when using strict diagnostic criteria. RLS is over 35% more prevalent in American women than their male counterparts.

A systematic review states 7.6% of the general population experiences sleep paralysis at least once in their lifetime. Its prevalence among men is 15.9% while 18.9% of women experience it. When considering specific populations, 28.3% of students and 31.9% of psychiatric patients have experienced this phenomenon at least once in their lifetime. Of those psychiatric patients, 34.6% have panic disorder. Sleep paralysis in students is slightly more prevalent for those of Asian descent (39.9%) than other ethnicities (Hispanic: 34.5%, African descent: 31.4%, Caucasian 30.8%).

MSbP is rare. A recent systematic study in Italy found that in a series of over 700 patients admitted to a pediatric ward, 4 cases met the diagnostic criteria for MSbP (0.53%). In this study, stringent diagnostic criteria were used, which required at least one test outcome or event that could not possibly have occurred without deliberate intervention by the MSbP person.

One study showed that in 93 percent of MSbP cases, the abuser is the mother or another female guardian or caregiver. This may be attributed to the prevalent socialization pattern that places females in the primary care-taking role. Of course, it could also be a gender trait rooted in genetics, as it is easy to see how females who seek attention as victims could gain an evolutionary advantage, while men seeking the same would be unfavoured for physical protection and mating. A psychodynamic model of this kind of maternal abuse exists.

MSbP may be more prevalent in the parents of those with a learning difficulty or mental incapacity, and as such the apparent patient could, in fact, be an adult.

Fathers and other male caregivers have been the perpetrators in only 7% of the cases studied. When they are not actively involved in the abuse, the fathers or male guardians of MSbP victims are often described as being distant, emotionally disengaged, and powerless. These men play a passive role in MSbP by being frequently absent from the home and rarely visiting the hospitalized child. Usually, they vehemently deny the possibility of abuse, even in the face of overwhelming evidence or their child's pleas for help.

Overall, male and female children are equally likely to be the victim of MSbP. In the few cases where the father is the perpetrator, however, the victim is three times more likely to be male.

Warning signs of the disorder include:

- A child who has one or more medical problems that do not respond to treatment or that follow an unusual course that is persistent, puzzling, and unexplained.

- Physical or laboratory findings that are highly unusual, discrepant with patient's presentation or history, or physically or clinically impossible.

- A parent who appears medically knowledgeable, fascinated with medical details and hospital gossip, appears to enjoy the hospital environment and expresses interest in the details of other patients' problems.

- A highly attentive parent who is reluctant to leave their child's side and who themselves seem to require constant attention.

- A parent who appears unusually calm in the face of serious difficulties in their child's medical course while being highly supportive and encouraging of the physician, or one who is angry, devalues staff and demands further intervention, more procedures, second opinions, and transfers to other more sophisticated facilities.

- The suspected parent may work in the health care field themselves or profess an interest in a health-related job.

- The signs and symptoms of a child's illness may lessen or simply vanish in the parent's absence (hospitalization and careful monitoring may be necessary to establish this causal relationship).

- A family history of similar or unexplained illness or death in a sibling.

- A parent with symptoms similar to their child's own medical problems or an illness history that itself is puzzling and unusual.

- A suspected emotionally distant relationship between parents; the spouse often fails to visit the patient and has little contact with physicians even when the child is hospitalized with a serious illness.

- A parent who reports dramatic, negative events, such as house fires, burglaries, or car accidents, that affect them and their family while their child is undergoing treatment.

- A parent who seems to have an insatiable need for adulation or who makes self-serving efforts for public acknowledgment of their abilities.

- A patient who inexplicably deteriorates whenever discharge is planned.