Using a structured pro forma, 728 out of 775 medical undergraduates at a Nigerian university were surveyed for the prevalence and pattern of drug use. An operational definition of substance abuse was made, and 28 percent of students fell within that criterion. Male abusers (81 percent) exceeded female abusers (19 percent). Substances most commonly abused were alcohol (60 percent), minor tranquilizers (48 percent), tobacco (35 percent), and narcotics (29 percent), particularly codeine. Only 11 percent abused cannabis. While most students were polydrug users, there was a low frequency of daily drug use. A general lifetime (occasional use) prevalence of substance use of 56 percent was found. Drugs consumed on a daily basis were alcohol (2 percent) and tobacco (6 percent). The prevalence of drug use was highest among the fourth and final year students. The majority of students were occasional abusers; there was no evidence of physical dependence.