BackgroundDespite the growing body of longitudinal research linking sleep problems and externalizing symptoms, regarding the direction of the effects of both variables, the results have been inconsistent. Given the mixed findings and inconsistent results in the literature, we propose that emotion dysregulation may link sleep problems and externalizing symptoms. MethodsThe participants (N = 1281, 49.65 % female; M = 12.73 years at time 1, SD = 0.68) were middle school students who completed assessments for sleep problems, externalizing symptoms, and emotion dysregulation. The interval between each wave was six months, for two consecutive years. Autoregressive mediation models using longitudinal data and cross-sectional mediation models using baseline data were evaluated and compared through structural equation modeling. ResultsThe results revealed that severe sleep problems (at T1, T2, or T3) were associated with higher levels of externalizing symptoms later in adolescence (at T2, T3, or T4), but not vice versa. In addition, analyses of indirect effects indicated that emotion dysregulation mediated this link, such that greater sleep problems led to more emotion dysregulation, which, in turn, led to more externalizing symptoms. ConclusionThe findings highlight the critical role that emotional regulation plays in the link between sleep problems and externalizing symptoms and emphasize the need for students as well as middle school administration to pay close attention to both the sleep and externalizing symptoms of early adolescents.