Abstract Background. The increasing prevalence of overweight among children in the United States presents a national health priority. Higher rates of overweight/obesity among minority women place their children at increased risk. Although increased rates of overweight are observed in 4- to 5-year-old children, they are not observed in 2- to 3-year-old children. Therefore, early prevention efforts incorporating families are critical. Methods. The primary aim of Hip-Hop to Health Jr. is to alter the trajectory toward overweight/obesity among preschool African-American and Latino children. This 5-year randomized intervention is conducted in 24 Head Start programs, where each site is randomized to either a 14-week dietary/physical activity intervention or a general health intervention. Results. This paper presents the rationale and design of the study. Efficacy of the intervention will be determined by weight change for the children and parent/caretaker. Secondary measures include reductions in dietary fat and increases in fiber, fruit/vegetable intake, and physical activity. Baseline data will be presented in future papers. Conclusions. The problem of overweight/obesity is epidemic in the United States. Behaviors related to diet and physical activity are established early in life and modeled by family members. Early intervention efforts addressing the child and family are needed to prevent obesity later in life. This paper describes a comprehensive, family-oriented obesity prevention program for minority preschool children.