Objective: The authors studied the relationship between a diagnosis of Attention-Deficit Hyperactivity Disorder (ADHD), grade point average (GPA), and licit and illicit drug use. Participants and Methods: They obtained survey data from a convenience sample of undergraduates in a large southern public university. Results: Among 1,550 respondents, 163 (10.5%) reported an ADHD diagnosis (ADHD Group). Of those without an ADHD diagnosis, 591 (43%) reported using prescription stimulants illicitly (No ADHD, Illicit Use group), and 794 (57%) reported not using prescription drugs illicitly (No ADHD, No Illicit Use group). The GPA of the ADHD group was significantly lower than the GPA of the other 2 groups. The ADHD group and the No ADHD, Illicit Use group reported significantly greater use of all other drugs than did the No ADHD, No Illicit Use group. Conclusions: Drug use was associated with a lower GPA in ADHD-diagnosed students than in students without ADHD.