The mediating influences of social support were examined in a study of 137 parents of mentally retarded, physically impaired, and developmentally at-risk children. Social system theory was used as a conceptual framework for assessing the effects of social support on personal well-being, parental attitudes toward their child, family integrity, parental perceptions of child functioning, parent-child play opportunities, and child behavior and development. A series of hierarchical multiple regression analyses by sets, controlling for family SES and income, child sex and age, and child developmental quotient and diagnosis showed that both satisfaction with support and number of sources of support had main and/or interactive effects in all sets of outcome measures. More supportive social networks were associated with better personal well-being, more positive attitudes, and more positive influences on parent-child play opportunities and child behavior and development. Findings were discussed in terms of both methodological and conceptual contributions to understanding the broad-based influences of social support.