We investigated longitudinal relations between children's sleep and symptoms of depression, anxiety, and anger/aggression. We expected that initial sleep problems and increases in these problems over time would be associated with worse adjustment outcomes. The study had 3 waves with 1-year lags. At Time 1 [T1], 128 girls and 123 boys (M age = 8.23 years, SD = 0.73) participated; M ages at Time 2 (T2) and Time 3 (T3) = 9.31 years (SD = 0.79) and 10.28 (SD = 0.99). The sample was diverse in relation to economic adversity and ethnicity (66% European and 34% African American). Higher initial levels and increases in sleep/wake problems or sleepiness over 3 years predicted higher levels of depression and anxiety symptoms at T3, controlling for T1 levels. These associations were more pronounced for girls, African American children, and children from lower socioeconomic status homes. Findings build on a small body of literature addressing links between sleep and adjustment longitudinally and highlight the importance of adequate sleep for children's optimal development, especially within the broader sociocultural milieu.