Forty-eight child psychotherapy outcome studies offering direct comparisons of an individual child treatment group to a combined parent-child/family therapy treatment group were included in this meta-analytic review. Results indicate that combined treatments produced a moderate effect beyond the outcomes achieved by individual child treatments, with an average weighted effect size that is within the medium range (d = 0.27). Moderator analysis indicated that, compared to non-cognitive-behavioral individual child treatments, cognitive-behavioral individual child treatments were closer in effectiveness to the overall more effective treatments that included parent participation. Results suggest that including parents in the psychotherapeutic treatment of children adds benefits beyond the outcomes achieved by individual child therapies. More research is needed on factors affecting parents' engagement and consistent participation in child psychotherapy treatment and on clinician's utilization of parents as therapy coparticipants. (Contains 2 tables, 1 figure, and 2 footnotes.)