Objective: To evaluate the efficacy of sleep hygiene and melatonin treatment for initial insomnia in children with attention-deficit/hyperactivity disorder (ADHD). Method: Twenty-seven stimulant-treated children (6-14 years of age) with ADHD and initial insomnia (greater than 60 minutes) received sleep hygiene intervention. Nonresponders were randomized to a 30-day double-blind, placebo-controlled, crossover trial of 5-mg pharmaceutical-grade melatonin provided by the study's sponsor. Results: Sleep hygiene reduced initial insomnia to less than 60 minutes in 5 cases, with an overall effect size in the group as a whole of 0.67. Analysis of the trial data able to be evaluated showed a significant reduction in initial insomnia of 16 minutes with melatonin relative to placebo, with an effect size of 0.6. Adverse events were generally mild and not different from those recorded with placebo treatment. The effect size of the combined sleep hygiene and melatonin intervention from baseline to 90 days' posttrial was 1.7, with a mean decrease in initial insomnia of 60 minutes. Improved sleep had no demonstrable effect on ADHD symptoms. Conclusion: Combined sleep hygiene and melatonin was a safe and effective treatment for initial insomnia in children with ADHD taking stimulant medication. (Contains 2 figures.)