• Social and behavioral characteristics of 11,966 British children, aged 5 years, and mothers' reports of accidental injuries between birth and age 5 years were analyzed. Aggressive behavior was associated with all accidental injuries after controlling psychosocial variables including social class; crowding; mother's psychological distress, age, and marital status; and child's sex. Overactivity was associated only with injuries not resulting in hospitalization after control of the covariates. The relative risk of injuries resulting in hospitalization was 1.9 among children with both high activity and high aggression scores compared with children with low scores on both behavioral scales. The findings support the inference that aggression and overactivity are independently associated with accidents. The associations between child behavior and injuries were stronger than the associations between injuries and the social factors including social class and crowding. This finding suggests that interventions aimed at high-risk groups may be effective supplements to environmental interventions.