Objective: Sleep disturbances are common in adults with attention-deficit/hyperactivity disorder (ADHD). In a case-control study, adult ADHD was associated with increased nocturnal motor activity and reduced self-perceived quality of sleep. Method: Eight adults with DSM-IV-diagnosed ADHD (combined type, N = 7; inattentive type, N = 1) were treated with stimulants in open-label form at 8:00 a.m., 12:00 noon, and 4:00 p.m. The mean daily dose was 51 mg of methylphenidate (range, 30-90 mg) in 7 subjects and 30 mg of dextroamphetamine in 1 subject. Actimeters were used to assess nocturnal motor activity during 6 consecutive nights both at baseline and after 3 weeks of treatment. The data were compared with those of 8 matched normal controls. Results: ADHD patients slept worse and showed significantly higher nocturnal motor activity at baseline compared with controls. No baseline differences between patients and controls were found in sleep latency, number of awakenings, and total time in bed. Changes from baseline to week 3 within the ADHD patients indicated improvement of sleep quality (p = .05) and reduction of Activity Level (p = .10) and Movement Index (p = .07) scores. When within-group changes were compared between ADHD subjects and controls, treatment with stimulants tended to be associated with a reduction of Activity Level (p < .01) and Movement Index (p = .04) scores and improved sleep quality (p =.02) in ADHD patients. Sleep latency, number of awakenings, and total time in bed were unaffected in withingroup and between-group analyses. Conclusion: The results should be interpreted cautiously given the open-label design and small sample size. Further study is warranted into the influence of stimulants on sleep in larger samples of ADHD patients by using controlled designs, multiple dose levels, and polysomnographic measures.