A B S T R A C TBackground: Individuals with Autism Spectrum Disorder (ASD) experience impairments in social communication, and these deficits often make it difficult to form and maintain friendships with peers. Poor sleep quality and daytime sleepiness are common among adolescents with ASD, and consequences of poor sleep may make social interactions difficult. Connections between sleep quality and social relationships in ASD samples have been understudied; the current study addresses this gap. Method: Participants were community samples of 19 adolescents with ASD and 10 neurotypical (NT) adolescents. Adolescents completed questionnaires about closeness and discord in relationships with a same-gender peer, and they reported on sleep-wake problems, daytime sleepiness, and internalizing problems. Adolescents also wore an actigraph for 7-nights. Results: Pearson correlations revealed significant associations between adolescents' reports of sleep problems and discordant peer relationships; more sleep-wake problems and more daytime sleepiness were associated with more discord with peers in the sample with ASD, but not in the NT sample. The closeness aspect of peer relationships was not significantly associated with sleep quality. Internalizing problems did not mediate between sleep quality and discordant relationships. Conclusions: Adolescents' reports of more sleep problems and daytime sleepiness, but not actigraph indicators of sleep quality, were directly associated with discordant peer relationships. Adolescents who are already challenged in social interactions due to ASD may be especially vulnerable to intense negativity in peer relationships when they also experience poorer nighttime sleep and more daytime sleepiness. NT adolescents may be better able to regulate social interactions despite poor sleep and feeling tired.