Objective: To examine associations between television viewing, sugar-sweetened beverage consumption, eating out, physical activity, and body weight change over 1 year. Design: Secondary data analysis from randomized intervention trial. Setting: Households in the community. Participants: Adults (n = 153) and adolescents (n = 72) from the same households. Intervention: Households were randomized to a home-based obesity prevention intervention or to a no-intervention control group for a 1-year period. Main Outcome Measures: Self-reported television viewing (TV) hours, diet, and physical activity. Body mass index (BMI) computed from measured weight and height (primary outcome measure). Analysis: Mixed-model regression. Results: Among adolescents, a significant prospective association was observed between decreases in television viewing hours and lower BMI z score at 1-year follow-up (decreased TV hours: BMI z score mean = 0.65; no change or increase TV hours: BMI z score = 0.92; P less than 0.02). No significant prospective associations were observed among adults. Conclusions and Implications: Reducing television viewing may be an effective strategy to prevent excess weight gain among adolescents. (Contains 4 tables.)