Insomnia subtypes have not been characterized in severely affected youth with autism spectrum disorder. We examined indices of clinical impairment (i.e. length of hospital stay, autism severity, nonverbal intelligence quotient, and adaptive and maladaptive behaviors) across insomnia subtypes in 427 psychiatrically hospitalized children with autism spectrum disorder (mean age = 12.8 ± 3.4; 81.3% male). Multivariate analysis with Bonferroni adjustment tested for differences in clinical impairment across insomnia subtypes adjusting for age and sex. Per parent report, 60% (n = 257) of children had at least one form of insomnia. The distribution of subtypes was sleep onset (26.1%, n = 67), sleep maintenance (24.9%, n = 64), early morning waking (4.3%, n = 11), and combined (44.7%, n = 115). There was a significant multivariate effect of insomnia subtypes on clinical impairment (Pillai's Trace = 0.25, F = 2.78, p < 0.001). Sleep maintenance and early morning waking were associated with longer hospital stays. Early morning waking was also associated with greater autism symptom severity. In general, children with sleep-maintenance or combined insomnias scored lower on adaptive behaviors and higher on maladaptive behaviors. Sleep-maintenance and combined insomnias appear to be more indicative of or consequential for impaired behavioral functioning.