Objectives: To examine whether excessive recreational Internet time, insufficient sleep, regular coffee consumption, or alcoholic beverages promote weight gain. Study design: A longitudinal cohort of >5000 girls (Growing Up Today Study), from all over the United States and aged 14 to 21 years, returned surveys in 2001 reporting typical past-year recreational Internet time, sleep, coffee (with caffeine), and alcohol consumption. We estimated correlations among these 4 exposures. Each girl also reported her height and weight in 2000 and again in 2001. Multivariate models investigated associations between 1-year change in body mass index and same-year exposures, adjusted for adolescent growth/development, activity, and inactivity. Results: The exposures were highly (P < .0001) correlated with each other, except for coffee with Internet time (P > .50). More Internet time, more alcohol, and less sleep were all associated (P < .05) with same-year increases in body mass index. Females, aged 18+ years, who slept ≤5 hours/night (P < .01) or who consumed alcohol 2+servings/week (P < .07) gained more body mass index from 2000 to 2001. For females in weight-promoting categories of all exposures, this translates to nearly 4 extra pounds gained over 1 year. We found no evidence that drinking coffee promotes weight gain. Conclusions: Older girls may benefit from replacing recreational Internet time with sleep and by avoiding alcohol.