Developing effective strategies to prevent childhood obesity is a public healthy priority. Opportunities for early intervention are important, and pediatric primary care is an appealing setting in which to base these efforts, given primary care providers' connection to children and families early in life. However, there is limited evidence to support the effectiveness of primary-care based prevention approaches; relatively few obesity prevention programs have been set in primary care and few have been rigorously evaluated. Healthy Homes/Healthy Kids (HHHK 5-10) is a randomized controlled trial developed to evaluate a primary-care based obesity prevention intervention. Four hundred and twenty one children (ages 5-10 years, mean=6.6) with BMI percentiles ranging from 70 to 95 (mean=84.8) and their parents were recruited from HealthPartners pediatric clinics. The intervention is ongoing, but we are using baseline data to investigate many questions of interest, and we are developing methods to assess intervention quality and delivery. Results from analyses on the following topics will be presented: 1) Parental styles and domain-specific practices as predictors of physical activity and sedentary behavior; 2) The relationship between parental concerns about child weight and family weight-related behaviors and characteristics; 3) Household variables and family behavior patterns associated with children meeting recommended guidelines for physical activity, fruit/vegetable intake, TV viewing, and avoidance of sugar-sweetened beverage; and 4) The fidelity and style of the HHHK intervention delivery. Results from these analyses will inform our understanding of factors that influence obesity, and this knowledge will be used to improve future interventions.