Background: Prior studies have had conflicting results regarding the relationship between adolescent depression and adult obesity. Objective: To test the hypothesis that depression in adolescence would increase the risk for obesity in early adulthood. Methods: We used data from a longitudinal study of a birth cohort of children born between April 1, 1972, and March 31, 1973, in Dunedin, New Zealand (N = 103 7). These data included regular diagnostic mental health interviews and height/weight measurements throughout childhood and adolescence. We performed logistic regression analyses to assess the relationship between major depression in early or late adolescence and the risk for obesity at 26 years of age. Results: Major depression occurred in 7% of the cohort during early adolescence (11, 13, and 15 years of age) and 27% during late adolescence (18 and 21 years of age). At 26 years of age, 12% of study members were obese. After adjusting for each individual's baseline body mass index (calculated as the weight in kilograms divided by the square of height in meters), depressed late adolescent girls were at a greater than 2-fold increased risk for obesity in adulthood compared with their nondepressed female peers (relative risk, 2.32; 95% confidence interval, 1.29-3.83). A dose-response relationship between the number of episodes of depression during adolescence and risk for adult obesity was also observed in female subjects. The association was not observed for late adolescent boys or for early adolescent boys or girls. Conclusions: Depression in late adolescence is associated with later obesity, but only among girls. Future studies should address reasons for these age and sex differences and the potential for intervention to reduce the risk for adult obesity in depressed older adolescent girls.