The incidence of Autism Spectrum Disorder ASD) is approaching epidemic proportions in the U.S. However, research has inadequately described how a family of a child with ASD functions as a system. Therefore, the hypothesized model examined the predictors of family functioning. A structural equation modeling SEM) approach was used to explore the relationship between childrens sleep problems and family functioning and the extent to which this relationship may be mediated by maternal stress. The model evaluated the strength of a direct relationship between childrens sleep problems and family functioning, as well as an indirect relationship that was mediated by maternal stress. Additionally the two groups, mothers of children with ASD ASD group) and mothers of typically developing children Community group), were analyzed to explore group differences. In both groups, maternal stress was predicted by childrens sleep: as mothers reported that their children exhibited more sleep problems, mothers reports of their stress levels also increased. Maternal stress was also predictive of family functioning. Specifically, there was a decrease in positive family functioning when mothers stress levels increased. Maternal stress mediated the relationship between childrens sleep problems and family functioning. Furthermore, the mediating relationship was stronger in the Community group than in the ASD group. The difference between groups may indicate that mothers of children with ASD are experiencing stress from multiple sources, aside from sleep problems, which may be contributing to their overall stress levels. Overall, findings suggested that childrens sleep problems contributed to the mothers stress levels and also to the overall family functioning. Future research should be designed to further explore families within a contextual framework and use a methodological approach that includes multiple measures of parent and family functioning and of childrens behaviors. In this way, a more comprehensive picture of families of children with ASDs can be developed that will inform the development of empirically based treatment approaches.