Schizophrenia is a disorder of a low incidence and relatively high prevalence and lifetime risk. The epidemiological evidence on its frequency and distribution in diverse populations is relatively consistent. Genetic predisposition, although a necessary factor, is not sufficient to explain its causation, and may itself be complex, involving interaction with environmental influences throughout development. Recent epidemiological studies using large databases and prospectively collected information have resulted in novel findings about antecedents and risk factors that may help in the integration of population-based approaches and molecular studies. Curr Opin Psychiatry 12:19-28. (C) 1999 Lippincott Williams & Wilkins.