We examined the relationship between parent-perceived neighborhood safety and children's physical activity, sedentary behavior, body mass, and obesity status using 9 years of longitudinal data (1999-2007) on a cohort of approximately 19,000 US kindergartners from the Early Childhood Longitudinal Study. Children's height and weight measurements and parent perceptions of neighborhood safety were available in kindergarten and in the first, third, fifth, and eighth grades. Dependent variables included age- and gender-specific body mass index percentile, obesity status, and parent- or child-reported weekly physical activity and television-watching. Pooled cross-sectional and within-child longitudinal regression models that controlled for child, family, and school characteristics were fitted. Both cross-sectional and longitudinal models indicated that children whose parents perceived their neighborhoods as unsafe watched more television and participated in less physical activity, although the magnitude of this association was much weaker in longitudinal models. However, there was no significant association between parent-perceived neighborhood safety and children's body mass index.