We evaluated a 12-week recreation center-based healthy lifestyle intervention for 30 obese home-dwelling young adults (YA) with intellectual disabilities. Three cohorts participated: YA only, YA and parents, and parents only. The YA cohorts received a nutrition/exercise intervention; parents focused on modeling healthy lifestyle behaviors. Outcomes included YA blood, nutrition, anthropometric, and fitness measures at pre, post, and 3-month follow-up. Compared with wait-list controls, the YA-only cohort improved immediately postintervention in blood pressure (BP), weight, and balance (p < .05). At 3-month follow-up, no intervention was consistently superior; overall reductions in weight, BP, hip circumference, and exercise barriers were obtained (p < .05). Linear and curvilinear changes from baseline to 3 months after the intervention varied by outcome and participant. Participants with Down syndrome lost less weight.