Driving performance of adult males with attention-deficit hyperactivity disorder (ADHD) was compared with matched controls in a double-blind (Ritalin vs. placebo) cross-over design, using a high-fidelity driving simulator. Seven ADHD and six non-ADHD drivers (mean age 22) were screened to rule out comorbidity and assess for ADHD, and then admitted to the General Clinical Research Center to control diet and sleep before testing. At 0800 and 1530, subjects consumed either a placebo or Ritalin pill in a counter-balanced manner, and at 0930 and 1700, subjects drove the simulator. After both drives, subjects rated their driving performance. Compared with non-ADHD subjects, ADHD subjects had more career driving accidents (p < .04) and motor vehicle violations (p = .059), drove worse on the simulator under placebo condition (p < .05), demonstrated significant improvement under the Ritalin condition (p < .05), rated themselves as driving poorer during the placebo condition (p = .05), and tended to perceive their driving to be better during the Ritalin condition (p = .07). This would suggest that individuals with ADHD should have the therapeutic benefit of a stimulant medication when operating a vehicle.