BACKGROUND: Pediatric primary care is an important setting for addressing obesity prevention. OBJECTIVE: The Healthy Homes/Healthy Kids 5-10 randomized controlled trial evaluated the efficacy of an obesity prevention intervention integrating pediatric primary care provider counseling and parent-targeted phone coaching. METHODS: Children aged 5 to 10 years with a BMI between the 70th and 95th percentile and their parents were recruited from pediatric primary care clinics. Participants received well-child visit provider counseling about obesity and safety/injury prevention and were then randomized to a 14-session phone-based obesity prevention (OP; n = 212) or safety and injury prevention contact control (CC; n = 209) intervention. The primary outcome was 12 and 24-month child BMI percentile. RESULTS: There was no overall significant treatment effect on child BMI percentile. Caloric intake was significantly lower among OP compared with CC participants at 12 months (P < .005). In planned subgroup analyses, OP condition girls had significantly lower BMI percentile (P < .05) and BMI z-score (P < .02) at 12 and 24 months relative to CC girls and were less likely to be overweight (38.0% vs 53.0%, P < .01) or (obese 3.4% vs 8.8%, P < .10) at follow-up. CONCLUSIONS AND RELEVANCE: An obesity prevention intervention integrating brief provider counseling and parent-targeted phone counseling did not impact 12 and 24-month BMI status overall but did have a significant impact on BMI in girls.