Economic and social change in the developing countries of Asia, Africa, Latin America, and the Pacific Islands is associated with increased rates of behavior-related illnesses, including psychiatric disorders, alcoholism, and substance abuse. Between 10 and 20 percent of the presenting problems in primary care settings in those countries are psychosocial. The authors provide an overview of the epidemiology of psychiatric and psychosocial morbidity in developing countries and summarize its effect on medical care systems in those settings. They suggest that American psychiatry increase its involvement in improving mental health care in developing countries. Consultation should be directed toward priorities determined locally in those countries, including assessment of current clinical practices, applied epidemiologic research, and training of indigenous researchers.