The current study aimed (1) to provide an analysis of the frequency and prevalence of sleep disturbances in a large Italian sample of children and adolescents with ASD, detecting specific predictors of the presence/absence of sleep disorders, (2) to examine the phenomenon of co-sleeping within a subgroup of participants with ASD. A total of 242 children and adolescents with ASD (194 males, mean age 5.03 ± 3.15years) were included. After the diagnostic procedure, caregivers were requested to complete the Sleep Disturbance Scale for Children (SDSC) to assess sleep disorders among participants. The presence of co-sleeping was investigated in a subgroup of 146 children and adolescents with ASD. An elevated or clinically relevant global score for sleep disorders (≥ 60) was found in 33% of participants. The most prevalent sleep disorder in our group was related to difficulties with sleep onset and sleep maintenance (~ 41% of cases). Sleep disturbances were predicted by higher intelligence quotient (IQ)/developmental quotient (DQ), increased internalizing problems, and elevated parental stress. The subgroup of participants engaged in co-sleeping (N = 87) were younger and had lower IQ/DQ scores, reduced adaptive functioning, and diminished psychological wellbeing than the non-co-sleeping group. Our findings are consistent with the current literature highlighting that insomnia is the most widespread sleep problem associated with ASD. The relationship between IQ/DQ and sleep alterations is a crucial topic that deserves additional research. Future studies should assess sleep by objective measures such as EEG topography to better understand the mechanisms underlying sleep alterations in this neurodevelopmental disorder.