OBJECTIVE: To examine the association between attention-deficit/hyperactivity disorder symptomatology and parent-reported sleep problems among preschoolers ages 2 to 5 years. METHOD: A total of 1,073 parents of preschoolers ages 2 to 5 years attending a large pediatric clinic completed the Child Behavior Checklist 1(1/2)-5 years. A stratified probability sample of 193 parents of high scorers and 114 parents of low scorers were interviewed with the Preschool Age Psychiatric Assessment. Poisson regression was used to test the association between parent-reported sleep problems and attention-deficit/hyperactivity disorder symptomatology, as well as psychiatric and demographic covariates. RESULTS: When considered without reference to other psychiatric disorders, elevated hyperactive-impulsive symptomatology was positively associated with parent reported problems including sleep assistance, parasomnias, and dyssomnias; however, all of these effects were attenuated to nonsignificance once psychiatric comorbidity was controlled. In contrast, elevated inattentive symptomatology (especially at lower levels of hyperactive-impulsive symptoms) was positively associated with daytime sleepiness even after psychiatric comorbidity was controlled. CONCLUSIONS: Neither hyperactive-impulsive nor inattentive attention-deficit/hyperactivity disorder symptomatology was uniquely related to parent-reported problems involving sleep assistance, parasomnias, or dyssomnias. However, inattentive symptomatology was uniquely related to daytime sleepiness above and beyond commonly occurring patterns of psychiatric comorbidity, sleep duration, and demographic factors.