An epidemiological study of alcohol use disorders was conducted on population samples from four aboriginal groups in Taiwan (a total of 993 subjects). The survey involved ethnographic observation and a semistructured psychiatric interview. The interview covered a detailed symptom profile that allowed diagnoses to be made according to different diagnostic criteria. The lifetime prevalences of alcoholism according to the ICD-10 (research criteria) and the DSM-III-R criteria were found to be 42.2-54.7% and 44.2-55.5%, respectively, much higher than the rates found in an earlier study (0.11-0.16%) conducted 40 years ago. Men in all groups were found to have higher prevalences, a lower mean age at onset, and a longer mean duration (except in one group) of alcoholism than women. Differences in the distribution of sociodemographic correlates (age, sex, marital status, education, and ethnicity) of ICD-10 harmful use of alcohol and alcohol dependence were examined by case-control analysis with logistic regression. The lifetime prevalences of alcohol use disorders were higher than in recent epidemiological surveys conducted elsewhere. Possible biological and sociocultural explanations for the high prevalence of alcoholism among the study populations are discussed.