Senior students at 23 regionally distributed medical schools received an anonymous questionnaire designed to examine current and prior use of tobacco, alcohol, and nine other drugs. The overall response rate was 67% (N = 2046). Substance use prevalence rates during the 30 days preceding the survey included alcohol, 87.5%; marijuana, 10.0%; cigarettes, 10.0%; cocaine, 2.8%; tranquilizers, 2.3%; opiates other than heroin, 1.1%; psychedelics other than LSD (lysergic acid diethylamide), 0.6%; amphetamines, 0.3%; barbiturates, 0.2%; LSD, 0.1%; and heroin, 0.0%. Compared with national, age-related comparison groups, senior medical students reported less use of all substances during the past 30 days and the past 12 months, except for alcohol, tranquilizers, and psychedelics other than LSD. Substantial new drug use after entry into medical school was reported only for tranquilizers. Seven students (0.2%) admitted to current dependence on a substance other than tobacco, four of these implicating marijuana. Thirty-three students (1.6%) believed that they currently needed help for substance abuse. Only 25.7% were aware of any policy on substance abuse at their own school.