In spite of inadequate laboratory demonstrations of sleep problems in children with attention deficit disorder with hyperactivity, the belief persists that such problems exist. Sleep restlessness is, in fact, one of the criteria in the Diagnostic and Statistical Manual of Mental Disorders, ed 3, definition of attention deficit disorder with hyperactivity, and sleep problems are listed on two major checklists often used for describing the symptoms of this disorder. In a series of three studies, sleep problems were investigated in preschool-aged children with attention deficit disorder relative to control children without the disorder. Results of the first two studies demonstrated clearly that parents of hyperactive children considered their children to have many more sleep problems than did parents of the control children. Parental daily documentation, which is less likely to be affected by reporting bias, was used in the third study. Although the results of the third study supported the finding of increased frequency of night wakings in these children, there was no difference in total sleep time or sleep onset latency between the two groups. Two other significant group differences (enuresis and night sweats) were primarily due to subgroups of children with attention deficit disorder and hyperactivity. The greater number of sleep wakings, which disrupt parents' sleep, may be responsible for the clinical reports that these children are poor sleepers.