Objective: To compare the effect of a once-daily extended-release methylphenidate formulation (PRC-063) versus placebo on sleep, measured via daily electronic diary in two clinical trials in pediatric (6-12 years) and adult ([greater than or equal to]18 years) patients with attention deficit hyperactivity disorder (ADHD). Method: A diary was completed by adult patients or parents/caregivers of pediatric patients during two randomized, double-blind, placebo-controlled laboratory classroom studies. Following dose optimization of PRC-063, patients were randomized to 1 week of double-blind treatment with PRC-063 or placebo before attending a full-day laboratory classroom session. Results: In the studies, 148 pediatric patients and 239 adult patients were randomized to either PRC-063 or placebo. When compared with the diaries of placebo patients, the sleep diaries in both pediatric and adult patients showed no statistical difference in total sleep time, efficiency, or latency. Conclusion: PRC-063 did not impact subjective measures of sleep versus placebo in pediatric and adult patients with ADHD.