Objective Sleep problems are frequent in children and robustly predict internalizing symptoms in adolescence and adulthood. Longitudinal investigations have nonetheless used broad measures of childhood sleep problems, precluding understanding of the specific sleep problems that presage affective disturbances. Similarly, prospective examinations of mechanistic variables linking early sleep with subsequent internalizing symptoms are lacking. Method Childhood bedtime and nighttime waking problems were examined as independent predictors of adolescent internalizing symptoms within a community sample from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (N = 1,089). The mediational role of emotional reactivity in late childhood also was examined. Results Bedtime but not nighttime waking problems significantly predicted adolescent internalizing problems. This relationship was partially explained by child emotional reactivity. Conclusions Some childhood sleep problems may more reliably predict later internalizing symptoms than others. Temperamentally based emotional reactivity may potentiate affective risk associated with childhood sleep difficulties.