STUDY OBJECTIVES: To assess the prevalence of illicit methylphenidate use among undergraduate college students at a large university, and to identify alcohol and other drug use behaviors, as well as the negative consequences and risk factors, associated with illicit methylphenidate use. DESIGN: Internet survey. SETTING: Large public university. SUBJECTS: Thirty-five hundred randomly selected undergraduate students. MEASUREMENTS AND MAIN RESULTS: Of the 2250 students who completed the survey, 3% reported past-year illicit methylphenidate use. Illicit methylphenidate users were significantly more likely to use alcohol and drugs and report adverse alcohol- and drug-related consequences than prescription stimulant users or students who did not use stimulants. Undergraduate men and women were equally likely to report past-year illicit methylphenidate use. Weekly party behavior was significantly associated with past-year illicit methylphenidate use. CONCLUSION: Illicit use of prescription-only stimulants on college campuses is a potentially serious public health issue. More work is needed to promote understanding and awareness of this problem among clinicians and researchers.