In a study of the severity of sleep disturbances in children with attention-deficit hyperactivity disorder (ADHD) who are taking stimulant medication, parents of 20 children diagnosed as having ADHD and on medication, 20 unmedicated children with some other psychiatric diagnosis (OPD), and 20 nonclinical control children responded to a 40-question structured interview to report the frequency of their children's sleep disturbances occurring during a 1-month interval. Parents of children in the ADHD group reported significantly more problems than parents of children in the other groups on variables within all three categories of behaviors: (a) settling and going to sleep, (b) disruptions during sleep, and (c) morning activities. From 25% to 50% of these parents reported very frequent difficulties in their children settling and going to sleep. These findings indicate that monitoring sleep-related behaviors and providing adjunctive therapies for sleep-related disturbances would be beneficial for many families with ADHD children who are taking stimulant medication.