Technical Abstract: OBJECTIVE: To test the efficacy of an innovative family-based intervention for overweight pre-school children and overweight parents conducted in the primary care setting. METHODS: 96 children with BMI >85th percentile and an overweight parent were randomized to Intervention or Information Control (IC). Trained staff delivered dietary and physical activity education to all parents over 6 months (10 group meetings and 8 calls). Parents in Intervention also received behavioral modification. An intention to treat analysis was performed using Mixed ANOVA models to test alterations in child % over BMI (%OBMI) and parent weight and to explore potential moderators of group differences in treatment response. RESULTS: Baseline characteristics did not differ between groups. Children in the Intervention group had greater %OBMI decreases at 3 and 6 months compared to those assigned to IC (p<0.0021). A greater BMI reduction over time was observed in parents in the Intervention group (p < 0.0001). Child %OBMI and parent BMI changes were correlated (r=0.31; p=0.003). Children with greater baseline %OBMI were more likely to have a greater %OBMI decrease over time (p =0.02).CONCLUSIONS: Concurrently targeting pre-school youth and their overweight parent for behavioral weight control in a primary care setting reduced child %OBMI and parent BMI, with parent weight loss predicting child weight change.