OBJECTIVE To evaluate the prevalence of insomnia and the treatments used by patients attending general practice clinics. DESIGN Survey of outpatients. SETTING Quebec city: Que, metropolitan area. PARTICIPANTS Two hundred eighteen patients recruited in the waiting rooms of general practice clinics. MAIN OUTCOME MEASURES Participants completed a survey on sleep and use of substances for insomnia, a questionnaire documenting their medical history and use of health care services, and three indices measuring presence of worry and symptoms of anxiety and depression. RESULTS Close to 38% of respondents suffered from insomnia: 26.2% had chronic insomnia and 11.4% had short-term insomnia. Prevalence was higher among women and people 35 to 54 years old. Among respondents who used substances to help them sleep, those 55 years and older consumed more prescription medications (benzodiazepines); those 35 to 54 pears old used mainly natural products; and those 16 to 34 years old consumed mainly over-the-counter medications. Respondents suffering from insomnia made heavier use of health care services and reported more worry and symptoms of anxiety and depression than those who slept well. CONCLUSIONS Patients attending general practice clinics have a high prevalence of insomnia. Physicians must be on the lookout for these sleep disturbances so they can offer appropriate treatment.