Rates of overweight in youth have reached epidemic proportions and are associated with adverse health outcomes. Family-based programs have been widely used to treat overweight in youth. However, few programs incorporate a theoretical framework for studying a family systems approach in relation to youth health behavior change. Therefore, this review provides a family systems theory framework for evaluating family-level variables in weight loss, physical activity, and dietary approaches in youth. Studies were reviewed and effect sizes were calculated for interventions that manipulated the family system, including components that targeted parenting styles, parenting skills, or family functioning, or which had novel approaches for including the family. Twenty-one weight loss interventions were identified, and 25 interventions related to physical activity and/or diet were identified. Overall, family-based treatment programs that incorporated training for authoritative parenting styles, parenting skills, or child management, and family functioning had positive effects on youth weight loss. Programs to improve physical activity and dietary behaviors that targeted the family system also demonstrated improvements in youth health behaviors; however, direct effects of parent-targeted programming is not clear. Both treatment and prevention programs would benefit from evaluating family functioning and parenting styles as possible mediators of intervention outcomes. Recommendations are provided to guide the development of future family-based obesity prevention and treatment programs for youth.