Objective: This study investigated the association between preschool children's sleep patterns measured by actigraphy and parent-reported hyperactivity symptoms. Many previous studies have reported sleep problems in children with attention deficit hyperactivity disorder (ADHD)-like symptoms. Methods: This study examined a cross-sectional sample of 186 preschoolers age 2-5 years in three groups: children with autism, children with developmental delay without autism, and typically developing children recruited from the general population. One week of actigraphic sleep data plus a parent report of the presence or absence of a current sleep problem were collected. Parents completed the child behavior checklist; a subset of children in preschool had teachers who completed the caregiver-teacher report form. Sleep behavior was compared for those children with and without clinical levels of attention-deficit/hyperactivity symptoms (T scores greater than or equal to 65). Results: The prevalence of a parent-defined sleep problem across the entire sample was 36.1%. Thirty-four percent of the sample had a parent-reported ADHD composite in the clinical range. Those children with a clinical ADHD profile were more likely to be described by parents as having a sleep problem. However, no significant differences in actigraphic sleep patterns or night-to-night sleep-wake variability were found for children with an ADHD profile in the clinical range. Conclusions: In this non-clinical sample of preschool age children, parental reports of clinical ADHD profiles were significantly associated with parental reports of sleep problems but not with actigraphically recorded sleep-wake data.