It was predicted that social cognitive, behavioral, and affective aspects of young children's social development would predict stable peer ratings of their likability. Measures of likability, emotion knowledge, prosocial and aggressive behavior, peer competence, and expressed emotions (happy and angry) were obtained for 65 subjects (mean age = 44 months). Sociometric ratings, particularly negative, were stable over 1- and 9-month time periods. Correlational analyses showed that emotion knowledge and prosocial behavior were direct predictors of likability. Prosocial behavior mediated the relations of gender and expressed emotions with likability (i.e., gender and expressed emotions were each related to prosocial behavior, and prosocial behavior was related to likability, but neither gender nor expressed emotions were related to likability with prosocial behavior partialled out). Knowledge of emotional situations similarly mediated the age-likability relation. Results uphold the early development of stable peer reputations and the hypothesized centrality of emotion-related predictors of likability.