The sleep profiles of 13 children with attention-deficit/hyperactivity disorder (ADHD) who were treated with a fixed dose of methylphenidate for at least 1 month were compared with those of 16 healthy siblings. Sleep disturbances were assessed according to a structured sleep questionnaire, and the severity of ADHD was evaluated via the Conners Parents Teachers Rating Scale. The results indicated that significantly more children with ADHD demonstrated single or multiple sleep disturbances as well as higher rates of specific sleep disorders, such as initial and middle insomnia, compared with their siblings. No correlation was found between the severity of ADHD and disturbed sleep. Sleep duration and satisfaction with sleep were similar in the two groups. These findings raise important questions regarding the association between ADHD and disturbed sleep.