Behavioral and emotional self-regulation are important aspects of competence in school-age children. Despite the apparent interrelatedness of behavioral and affective processes, empirical approaches to the development of self-regulation typically have investigated these systems separately. As a result, their relative effects upon social competence remain, for the most part, an open question. This study, working from an organizational and developmental psychopathology perspective, attempted to investigate developmental processes that place maltreated children at risk for impaired peer relationships by assessing the independent and relative influences of behavioral and emotional regulation on social competence in school-age children. Subjects were maltreated children, who are at risk for both attenuated self-regulation and impaired peer relationships, and economically disadvantaged nonmaltreated comparison children. Observations were conducted during a summer day camp, an ecologically valid context in which to study children's social interactions. As predicted, maltreated children were found to be deficient in behavioral and affective regulation, relative to nonmaltreated children. Furthermore, attenuated self-regulation mediated the effects of maltreatment on children's social competence. Results highlighted the unique contributions of both behavior and affect in predicting peer competence, suggesting that a more comprehensive approach to the study of self-regulation is warranted.