This study examined the impact of low birth weight on children's health and assessed the influence of the social environment on various aspects of health in low birth weight and normal birth weight children. Data on 8661 children aged 2 through 11 from the 1981 Child Health Supplement of the National Health Interview Survey provided strong evidence for two major conclusions: (1) Low birth weight children in high-risk social environments are at increased for poor health outcomes compared with comparable normal birth weight children. This vulnerability was found across all age groups, suggesting that the effects of low birth weight are long-lasting. The poor health outcomes for low birth weight children in high-risk social environments were found for all seven aspects of child health status studied: excessive bed days, restricted-activity days, and school-loss days; school failure, low school-ranking, behavior problems, and maternal perception of child health status as fair/poor. (2) The mechanism of risk was complex and differed by birth weight group. Whereas certain combinations of individual risk factors protected normal birth weight children from several adverse outcomes, none for low birth weight children were identified. However, low birth weight children in low- or moderate-risk social environments were not at greater risk for poor outcomes compared with comparable normal birth weight children. This study underscores the importance of a healthy social environment for children who are already at high risk for poor health outcomes by virtue of being low birth weight.