Several large surveys have suggested high prevalence of psychiatric disorders among gay men and other men who have sex with men.In 2002, a comprehensive health survey was conducted among 571 gay men in Geneva, Switzerland, using probability-based time-space sampling. The Composite International Diagnostic Interview Short-Form (CIDI-SF) was used to assess 12-month prevalence of major depression, specific phobia, social phobia, alcohol dependence, and drug dependence.Nearly half (43.7%, 95% CI=39.0-48.4) of the sample fulfilled the criteria for at least one of the five DSM-IV disorders: 19.2% had major depression, 21.9% had specific and/or social phobia, and 16.7% had an alcohol and/or drug dependence disorder in the past 12 months. Over one quarter of the cases were comorbid with another kind of disorder, and 35.7% of cases consulted a health care professional in the past 12 months for mental health. Like cases, screen-positives for mood and/or anxiety disorders (24.7%) also reported significantly greater disability and lower quality of life.Nearly two-thirds of this community sample of gay men was affected by psychiatric morbidity with new evidence for comorbidity, subthreshold disorders, and low levels of awareness of psychiatric disorders and their treatment. This population needs to be a priority in psychiatric epidemiology and mental public health.