Objectives. To evaluate bidirectional associations between obesity and depressed mood in adolescent girls, and determine if associations differed by racial/ethnic group. Methods. We analyzed data collected from 918 adolescent girls studied in 6th and 8th grades in the Trial of Activity for Adolescent Girls (TAAG). Racial/ethnic group was defined as non-Hispanic white, non-Hispanic black, and Hispanic. Height and weight were measured and obesity was defined as a body mass index-for-age ≥95th percentile. The Center for Epidemiologic Studies Depression Scale (CES-D) was used to measure depressive symptoms and depressed mood, defined as CES-D ≥24. Generalized estimating equations were used to examine associations between 6th grade obesity and 8th grade depressed mood, as well as 6th grade depressed mood and 8th grade obesity. Results. Racial/ethnic group was a statistically significant effect modifier in both directions of association (p<0.02). Among white girls, 6th grade obesity was associated with greater likelihood of depressed mood in 8th grade (odds ratio [OR]=2.47, 95% confidence interval [CI]: 1.85, 3.30), whereas for black and Hispanic girls this association was not observed (OR= 1.16 and 0.82, respectively). Also for white girls, 6th grade depressed mood was associated with greater likelihood of obesity in 8th grade (OR = 4.47, CI: 1.96, 10.24), whereas for black and Hispanic girls, OR=0.83 and 1.89, respectively. Conclusions. Associations between obesity and depressed mood may be most problematic among adolescent girls in the white racial/ethnic group. Our results are consistent both with depressed mood contributing to obesity and obesity contributing to depressed mood.