This study examined the extent to which effortful control moderated the risk of internalizing or externalizing problems associated with high negative emotionality in a Dutch population sample of pre- and early adolescents (N = 1,922). Internalizing and externalizing problems were assessed with the Child Behavior Checklist, Youth Self-Report, and Teacher Checklist of Psychopathology. Temperament (effortful control, fearfulness, frustration) was assessed with the parent version of the Revised Early Adolescent Temperament Questionnaire. The effects of fearfulness and frustration appeared to be attenuated by high levels of effortful control. The associations differed between the two domains of mental health investigated: effortful control reduced the effect of fearfulness on internalizing problems and the effect of frustration on externalizing problems. The effects were stronger for externalizing problems and similar for preadolescent (age 11) and adolescent (age 13/14) outcomes.