Sociometrics and teacher ratings of hyperactivity and aggression were obtained on 390 boys in grades 1- 6 to explore the relative contributions of hyperactivity and aggression to children's social adjustment. Both hyperactivity and aggression were correlated with negative sociometric nominations at all grade levels; however, only hyperactivity showed consistent inverse correlations with positive sociometric nominations. In multiple regression analyses, hyperactivity contributed incremental variance to the prediction of problematic sociometric status at all grade levels, while aggression did so only at grades 3- 4. An examination of the core symptoms of hyperactivity revealed that motor hyperactivity, in the absence of impulsivity and inattention, did not predict negative sociometric status at any grade level. Subgroups of boys categorized as hyperactive only, aggressive only, hyperactive/aggressive, and nonhyperactive/nonaggressive controls were compared on teacher ratings and sociometrics. Hyperactive/aggressive boys had higher hyperactivity and aggression ratings than boys in either of the single- problem groups; all three behavior problem groups had more negative social status than controls. Developmental changes in children's normative expectations for social behavior were discussed as possible mechanisms mediating the age- related differences in relations among aggression, hyperactivity, and peer relations.