Introduction:The current study tested the longitudinal bidirectional links between changes in sleep quality and two measures of internalizing problems, depressive and anxiety symptoms, and whether these links differed between males and females. Methods: Longitudinal data were collected from 570 early adolescents (58.6% female; M age = 12.43 years, SD = 0.66 at Time 1) who were assessed four times over the course of 1.5 years. Results: Cross-lagged panel models were hypothesized and tested the bidirectional links between sleep quality and both depressive and anxiety symptoms; multigroup tests were used to test for sex differences. Sleep quality and developmental changes in sleep quality were negatively associated with developmental changes in depressive symptoms as well as anxiety symptoms over time, and vice versa. These associations did not differ between male and female early adolescents. Conclusions: Study findings provide evidence that the relationship between poor sleep quality and depressive symptoms as well as anxiety symptoms are likely bidirectional and consistently intertwined. Clinicians might consider both problems to better guide case conceptualization and treatment.