Background and purpose: Sleep disturbances in autism spectrum disorder (ASD) are common and may impair daytime functioning as well as add to parental burden. In this well characterized sample of young children with ASD and disruptive behaviors, we examine the association of age and IQ in sleep disturbances using the Child Sleep Habits Questionnaire modified for ASD (CSHQ-ASD). We also test whether children with poor sleep have greater daytime behavioral problems than those with better sleep. Finally, we examine whether parental stress is higher in children with greater disruptive behaviors and sleep disturbances. Participants and methods: One hundred and seventy-seven children with complete data out of 180 (mean age 4.7) with ASD participated in a randomized clinical trial. Parents completed the CSHQ-ASD and several other measures at study enrollment. The sample was divided into “poor sleepers” (upper quartile on the total score of the CSHQ-ASD) and “good sleepers” (lower quartile) for comparisons. Analyses were conducted to evaluate group differences on age, IQ, daytime disruptive behavior, social disability and parental stress. Results: The two groups of young children with ASD, good sleepers versus poor sleepers, were not different on age or cognitive level. Children in the poor sleeping group had significantly higher daytime behavioral problems including irritability, hyperactivity, social withdrawal and stereotypical behaviors. Parents in this group reported significantly higher levels of stress. Conclusions: The finding of no age difference between good and poor sleepers in young children with ASD and disruptive behaviors suggests that sleep problems are unlikely to resolve as might be expected in typically developing children. Likewise, the good and poor sleepers did not significantly differ in IQ. These findings add strong support for the need to screen for sleep disturbances in all children with ASD, regardless of age and cognitive level. Poor sleepers exhibited significantly greater daytime behavioral problems and parents of children in this group reported significantly higher levels of stress. Above and beyond the co-occurring disruptive behavior, poor sleep quality appears to pose substantial additive burden on child and parents.