Abstrak: By using data from wave 2 (in 1996) and wave 3 (in 2000-2001) of the US-based National Longitudinal Study of Adolescent Health, we investigated the association between young women's body weight and depression during the transition to adulthood. Respondents (n = 5,243) were 13-18 years of age during wave 2 and 19-25 years of age during wave 3. We used Center for Epidemiologic Studies Depression Scale scores to classify young women as never depressed, consistently depressed, experiencing depression onset, or experiencing depression recovery from wave 2 to wave 3. Results from adjusted multinomial logistic regression models indicated that respondents who experienced significant weight gain were at risk of depression onset. Normal weight (adjusted odds ratio = 2.10, 95% confidence interval: 1.14, 3.84) and overweight (adjusted odds ratio = 1.86, 95% confidence interval: 1.15, 2.99) adolescent girls who were obese by young adulthood, as well as young women who were consistently obese during adolescence and young adulthood (adjusted odds ratio = 1.97, 95% confidence interval: 1.19, 3.26), had roughly twice the odds of depression onset as did young women who were never overweight. We concluded that weight gain and obesity are risk factors for depression onset during the transition to adulthood. Policies prioritizing healthy weight maintenance may help improve young women's mental health as they begin their adult lives.