Relational aggression (RA), thought to be more typical of females, is a form of aggression in which relationships are used as vehicles of harm (Crick & Grotpeter, 1995). This study investigated sex-differences in the prevalence of RA and physical aggression (PA), as well as the group and friendship relations of relationally and physically aggressive children. It was predicted that (a) girls would be rated as more relationally aggressive than boys when extreme group scores of RA were examined; (b) boys would be rated as more relationally aggressive than girls when continuous measures of RA were used; (c) boys would be higher than girls in PA regardless of the assessment measure; and (d) girls would use more RA than PA, whereas boys would use more PA than RA. It was also predicted that (e) relationally aggressive boys and physically aggressive girls would be at heightened risk for peer rejection; (f) aggressive children would have mutual friendships in spite of their lack of popularity; (g) relationally and physically aggressive children would have similarly aggressive friends; and (h) RA and PA would predict lower-quality friendships.