The aim of this study was to investigate the toddler and preschool predictors of early peer social preference. Behavioral and social functioning were examined in a sample of children across the toddler and preschool years from parent and teacher observations. Kindergarten social behavior and peer social preference were assessed in the children's kindergarten classrooms using standard sociometric techniques. Results indicated that parent report of toddler externalizing behavior and teacher report of preschool problem behavior, as indexed by aggressive behavior, social skills, and emotional regulation, were predictive of peer liking in kindergarten. However, this relation was mediated by specific behaviors evidenced in the kindergarten classroom. For boys, overt aggression mediated these relations. For girls, sharing and engaging in sneaky behavior in kindergarten mediated the relation between preschool problem behaviors and peer status. These results indicate that specific behaviors displayed in the peer group account for the relation between early problem behavior and peer status. Moreover, these data point to the importance of considering gender when examining developmental trajectories and outcomes.