AbstractObjectiveAmerican Indian children of pre-school age have disproportionally high obesity rates and consequent risk for related diseases. Healthy Children, Strong Families was a family-based randomized trial assessing the efficacy of an obesity prevention toolkit delivered by a mentorv. mailed delivery that was designed and administered using community-based participatory research approaches.DesignDuring Year 1, twelve healthy behaviour toolkit lessons were delivered by either a community-based home mentor or monthly mailings. Primary outcomes were child BMI percentile, child BMIZ-score and adult BMI. Secondary outcomes included fruit/vegetable consumption, sugar consumption, television watching, physical activity, adult health-related self-efficacy and perceived health status. During a maintenance year, home-mentored families had access to monthly support groups and all families received monthly newsletters.SettingFamily homes in four tribal communities, Wisconsin, USA.SubjectsAdult and child (2–5-year-olds) dyads (n150).ResultsNo significant effect of the mentoredv. mailed intervention delivery was found; however, significant improvements were noted in both groups exposed to the toolkit. Obese child participants showed a reduction in BMI percentile at Year 1 that continued through Year 2 (P<0·05); no change in adult BMI was observed. Child fruit/vegetable consumption increased (P=0·006) and mean television watching decreased for children (P=0·05) and adults (P=0·002). Reported adult self-efficacy for health-related behaviour changes (P=0·006) and quality of life increased (P=0·02).ConclusionsAlthough no effect of delivery method was demonstrated, toolkit exposure positively affected adult and child health. The intervention was well received by community partners; a more comprehensive intervention is currently underway based on these findings.