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Obsessions are unwanted aversive cognitive experiences usually associated with feelings of dread, loathing, or a disturbing sense that something is not right. The individual recognizes (at some point in time) that these concerns are inappropriate in relation to reality and will generally attempt to ignore or suppress them. Compulsions are overt behaviors or covert mental acts performed to reduce the intensity of the aversive obsessions. They may occur as behaviors that are governed by rigid, but often irrelevant, internal specifications. They are inappropriate in nature or intensity in relation to the external circumstances that provoked them.

A. Epidemiology

1. Population frequencies

Lifetime prevalence rates of obsessive–compulsive disorder (OCD) in the United States range between 2% and 3%, but may be slightly lower in certain ethnic subgroups, including African Americans and possibly Hispanics. Lifetime prevalence rates are similar (approximately 2%) in Europe, Africa, Canada, and the Middle East, but appear to be lower (0.5–0.9%) in certain Asian countries (i.e., India and Taiwan). Lower prevalence rates in selected U.S. and other national populations could be related to cultural factors resulting in underreporting of symptoms, or be related to such biological factors as increased resistance to basal ganglia disease. Although OCD is thought to be a lifetime illness, lifetime prevalence rates in young adults are more than twice those seen in the elderly. It is unclear whether this observation represents a reporting bias, a waning of symptoms with advancing age, a shorter life expectancy in patients with OCD, or a changing environmental factor relating to the etiology of the illness.

OCD is usually first seen in childhood or early adulthood: 65% of patients have their onset before age 25 years, 15% after the age of 35 years, and 30% in childhood or early adolescence. In the last population, there is a 2:1 preponderance of males; in contrast, OCD in the adult population is slightly more predominant in women. The frequency of OCD in psychiatric practice may be significantly lower than in the general population. Indeed, the incidence of OCD was previously thought to be as low as 0.05% based on psychiatric samples. Low frequency estimates may be related to the intense shame and secrecy associated with this illness and the patients' reluctance to divulge their symptomatology.

The frequency of specific obsessions and compulsions is fairly constant across populations. Contamination fears are present in approximately 50% of OCD patients, unwarranted fears that something is wrong (called pathologic doubt) in 40%, and other obsessions, including needs for symmetry, fears of harm to self or others, and unwanted sexual concerns, in 25–30%. Checking and decontamination rituals are the predominant rituals in OCD (50–60%). Other rituals, such as arranging, counting, repeating, and repetitive superstitious acts, occur less frequently (30–35%). Most patients with OCD (60%) have multiple obsessions or compulsions.

2. Population subtypes

The only ...

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