This US-based study investigated individual and joint associations of the home environment and the neighbourhood-built environment with adolescent dietary patterns and body mass index (BMI) z-score. Data were analysed from 2682 racially/ethnically and socioeconomically diverse adolescents (53.2% girls; mean age 14.4 years) attending Minnesota middle and high schools who participated in the EAT (Eating and Activity in Teens) 2010 study. Study participants completed height and weight measurements and surveys. In multiple regression analyses, supportive family environments (i.e., higher family functioning, frequent family meals, and parent modelling of healthful eating) were associated with higher adolescent fruit and vegetable intake, lower fast food consumption, and lower BMI z-score. Fewer associations were observed between the built environment and adolescent outcomes. Evidence indicated that the relationship between a supportive family environment and adolescent fruit and vegetable intake and BMI was enhanced when the neighbourhood was supportive of healthful behaviour.