Internalizing psychopathology, including depression and anxiety, has been associated with sleep-wake problems among youth. Although transdiagnostic theories of psychopathology posit that emotion dysregulation explains many of the symptoms associated with internalizing psychopathology, examination of regulatory mechanisms underlying this association is limited, particularly during the transition to early adolescence when risk for affective dysregulation and sleep-wake problems is heightened. Using a longitudinal design with a youth community sample (N = 278), the current study found a positive, indirect effect of internalizing psychopathology (x-bar[subscript age] = 9.84) on later sleep-wake problems (x-bar[subscript age] = 14.53) via higher levels of a more maladaptive emotion regulation strategy (i.e., expressive suppression), with no evidence of an indirect effect of a more adaptive strategy (i.e., cognitive reappraisal; x-bar[subscript age] = 12.02). Findings have important clinical implications for targeting the reduction of maladaptive emotion regulation strategies, such as expressive suppression, in order to address sleep problems among youth with internalizing psychopathology.