Objective To examine the effectiveness of a family-based behavioral group intervention (Positively Fit; PF) for pediatric obesity relative to a brief family intervention (BFI) in a sample of treatment-seeking children and adolescents. Methods Families (n = 93) were randomized to treatment condition. Assessments were conducted at pre- and posttreatment and at 12-month follow-up. Outcome indices included standardized body mass index (BMI) and quality of life (QOL). Results Results indicated a significant reduction in zBMI at posttreatment and follow-up across both conditions. At follow-up, BFI and PF participants evidenced average reductions of .12 and .19 zBMI units, respectively. Children demonstrated better outcomes than adolescents across both conditions. Results indicated clinically significant improvements in parent-reported QOL at postintervention and in self-reported QOL at follow-up for PF participants. Conclusions Results suggest the effectiveness of family-based interventions for pediatric obesity in clinical settings among younger children. Neither intervention was effective in terms of reducing zBMI among adolescents.