Nonmedical use of prescription stimulants and analgesics was assessed from personal interviews with a stratified random sample of 1,253 first-year college students aged 17 to 20 attending a large public university (86% response rate). Lifetime and past-year prevalence of nonmedical use of stimulants and/or analgesics was 19.6%(wt) and 15.5%(wt), respectively. Nonmedical users had significantly lower grade point averages (GPAs) in high school as compared with nonusers; in college they skipped classes more often, spent more time socializing, and spent less time studying. For example, nonmedical users of both stimulants and analgesics skipped 21% of their college classes whereas nonusers skipped 9%. Controlling for high school GPA and other factors, past-year nonmedical use independently predicted lower college GPA by the end of the first year of college; this effect was partially mediated by skipping more classes. Nonmedical users of prescription drugs comprise a high-risk group for academic problems in college.