This study compared the peer functioning of a community sample of preschool boys with pervasive hyperactivity (N=33) and comparison boys (N=34), and examined the extent to which any differences in peer functioning between these groups could be explained by comorbid child conduct problems and parenting factors. The quality of boys’ peer relations was assessed on the basis of teacher and observer ratings of peer-related behavior at preschool. The quality of parenting and boys’ behavior at home were assessed using the Parental Account of Children's Symptoms Interview, the Parenting Scale, and videotaped mother–son interactions. Boys with hyperactive behavior problems showed higher rates of aggressive, noncompliant, and nonsocial behaviors, and lower rates of prosocial behavior and peer acceptance than boys in the comparison group. These between-group differences in social functioning remained significant following statistical control for the effects of conduct problems, highlighting the wide range of peer difficulties associated with preschool hyperactivity. Results of further analyses suggest that the quality of early mother–child interactions and the behavioral features of hyperactivity may make unique contributions to the 00development of peer relationship difficulties in preschool children with pervasive hyperactivity.