This study investigated both relational and physical aggression in preschool children, explored potential differences in informant reporting and child sex on these subtypes, and examined relationships between types of aggressive behaviors and other types of negative and positive social behaviors. Naturalistic observations of social behavior, teacher ratings, and peer reports were used to assess 67 children's (35 female) behaviors. Evidence was found for the existence of both relational and physical aggressive behavior in preschool children, although observers infrequently identified relational aggression. Categorization of children into a preferred style of aggression differed between informants, with more behavioral observers than teachers characterizing children as displaying only one type of aggression. Results also showed that reports were correlated between informants for physical aggression but not for relational aggression. Sex differences emerged for children's levels of physical aggression but not for relational aggression. Both physical and relational aggression were associated with ratings of problem behaviors in general; however, only physical aggression was negatively related to positive aspects of social functioning.