BACKGROUND: Children and adolescents with autism spectrum disorder (ASD) have difficulties that limit their opportunities to interact with peers and family members. These behaviors can lead to social exclusion, and consequently social isolation. The aim was to compare social isolation of children and adolescents with ASD according to age, marital status, and number of siblings. MATERIALS AND METHODS: Cross-sectional descriptive study in 37 subjects with ASD. Social isolation was assessed using a 6-item scale (with five alternatives). The sociodemographic variables were age, sex, marital status of parents, and number of siblings. Two groups were formed according to age (children from 4 to 10 years old and adolescents from 11 to 20 years old). RESULTS: For the total score of the social isolation scale, children showed a higher score (21.1 ± 4.7) than adolescents (17.7 ± 5.7). Children living with divorced parents had lower scores (16.2 ± 3.6), compared to married (22.2 ± 4.5) and cohabiting (22.8) children. For the number of siblings, with no siblings 17.2 ± 3.1 points, one sibling 22.2 ± 3.5 points, two siblings 22.1 ± 3.1 points, and three siblings 22.4 ± 3.2 points (P < 0.05). Age was related to social isolation (r = −0.30, P < 0.05). CONCLUSION: Children who live with divorced parents and have no siblings presented a higher degree of isolation in relation to their counterparts who live with both parents and have at least one sibling. Age plays a relevant role, with children aged 4–10 years presenting a lower degree of isolation than the adolescent group. It is suggested that the preservation of a functional family and the presence of siblings could contribute to improving social isolation.