Given the continuing rise of the U.S. Hispanic population, reversing the Hispanic childhood obesity epidemic is critical to the nation's future health. Mexican American children and those from socioeconomically disadvantaged families often are far more overweight and obese than their peers, heightening their risk for obesity-related health complications. Our proposed randomized controlled trial, the Health4Kids (H4K) Trial for Hispanic Families, aims to improve Hispanic children's body composition by testing a comprehensive, culturally and linguistically relevant, family-oriented intervention for overweight and obese (body mass index (BMI) between the 85th and 99.9thth (<99th) percentile for age and gender) Hispanic children ages 6-11 in pediatric clinics in San Antonio, Texas, a largely Hispanic city. Our team, formed during our pilot research funded by the Centers for Medicare and Medicaid Services (1H0CMS030457), unites academic investigators and community partners with experience working together to conduct behavioral and clinical interventions and outreach with Hispanics. The H4K trial will test the efficacy of a 6-month pediatric obesity management intervention (physician counseling plus telephone counseling, newsletters and text messages) compared to standard care (physician counseling only) on three outcomes: 1) body composition (i.e., waist circumference, weight and z-BMI); 2) insulin, glucose and cholesterol levels; and 3) behavior change in physical activity (PA), sedentary behavior and consumption of sugary beverages and fruits and vegetables. We will recruit 230 overweight and obese children—and a parent or guardian for each—and randomize them to the POM intervention (n = 115 child/parent dyads) or standard care (n = 115 child/parent dyads). From a baseline, we will measure the impact of the trial on the primary outcome (body composition) and secondary outcomes (insulin, glucose and cholesterol levels and several specific health behavior changes) at 1 month, 6 and 12 months post-randomization. We also will evaluate the critical role of parenting strategies and changes in the home environment as mediators of intervention effects. We hypothesize that intervention children will significantly improve their body composition, increased their PA levels and diet quality (more fruits and vegetables and less sugary beverages), and decrease their sedentary activity, compared to children in standard care. If successful, this study will generate new scientific knowledge about effective Hispanic family-based approaches for obesity prevention with high potential for replication in underserved areas across the nation.