ABSTRACT: Background/Aims Few obesity prevention trials have focused on young children and their families in the home environment, particularly in underserved communities. Healthy Children, Strong Families 2 is a randomized controlled trial of a healthy lifestyle intervention for American Indian children and their families, a group at very high risk of obesity. The study design resulted from our long-standing engagement with American Indian communities, and few collaborations of this type resulting in the development and implementation of a randomized clinical trial have been described. Methods Healthy Children, Strong Families 2 is a lifestyle intervention targeting increased fruit and vegetable intake, decreased sugar intake, increased physical activity, decreased TV/screen time, and two less-studied risk factors: stress and sleep. Families with young children from five American Indian communities nationwide were randomly assigned to a healthy lifestyle intervention ( Wellness Journey) augmented with social support (Facebook and text messaging) or a child safety control group ( Safety Journey) for 1?year. After Year 1, families in the Safety Journey receive the Wellness Journey, and families in the Wellness Journey start the Safety Journey with continued wellness-focused social support based on communities' request that all families receive the intervention. Primary (adult body mass index and child body mass index z-score) and secondary (health behaviors) outcomes are assessed after Year 1 with additional analyses planned after Year 2. Results To date, 450 adult/child dyads have been enrolled (100% target enrollment). Statistical analyses await trial completion in 2017. Lessons learned Conducting a community-partnered randomized controlled trial requires significant formative work, relationship building, and ongoing flexibility. At the communities' request, the study involved minimal exclusion criteria, focused on wellness rather than obesity, and included an active control group and a design allowing all families to receive the intervention. This collective effort took additional time but was critical to secure community engagement. Hiring and retaining qualified local site coordinators was a challenge but was strongly related to successful recruitment and retention of study families. Local infrastructure has also been critical to project success. Other challenges included geographic dispersion of study communities and providing appropriate incentives to retain families in a 2-year study. Conclusion This multisite intervention addresses key gaps regarding family/home-based approaches for obesity prevention in American Indian communities. Healthy Children, Strong Families 2's innovative aspects include substantial community input, inclusion of both traditional (diet/activity) and less-studied obesity risk factors (stress/sleep), measurement of both adult and child outcomes, social networking support for geographically dispersed households, and a community selected active control group. Our data will address a literature gap regarding multiple risk factors and their relationship to health outcomes in American Indian families.