The current study examines how gender discrimination by adults in school is linked with depressive symptoms and sleep duration over time in middle school. The main goal is to test one psychological mechanism that can account for such associations: perceived school unfairness. Relying on a racially-ethnically diverse sample of girls (N = 2,718, M[subscript age] = 13.01, SD[subscript age] = 0.39) from 26 middle schools, multilevel mediation analyses revealed that girls who experienced school-based gender discrimination by an adult in seventh grade reported higher levels of perceived school unfairness in eighth grade. Moreover, perceived unfairness, in turn, was associated with more depressive symptoms and shorter sleep durations by eighth grade. Implications of changes in adolescent girls' sleep and mood related to their experiences of gender discrimination are discussed.