OBJECTIVE : To explore whether paternal psychological distress is related to the longitudinal course of child problem behavior after accounting for maternal psychological distress. METHODS : We used data from the Millennium Cohort Study (MCS), a large general-population birth cohort in the United Kingdom. Maternal and paternal psychological distress was measured with the Kessler 6-item Psychological Distress Scale (K-6) at child ages 3, 5, 7, 11, and 14 years. Problem behavior was measured with the Strengths and Difficulties Questionnaire at these ages. Data were analyzed using growth curve modeling, before and after adjustment for confounders (N = 13,442). RESULTS : The effect of paternal psychological distress was weaker than that of maternal psychological distress. However, even after adjustment for maternal psychological distress and confounding, paternal psychological distress predicted all four domains of child problem behavior that we examined (hyperactivity, conduct, emotional, and peer problems). Child problem scores were generally lower in biological father families, but the effect of paternal psychological distress was the same for children in biological and nonbiological father families and did not depend on the level of maternal psychological distress. High levels of paternal psychological distress predicted some problems (emotional symptoms and hyperactivity) more strongly in boys than in girls. CONCLUSIONS : There was evidence for a robust association between psychological distress in fathers and problem behavior in their offspring. Our findings suggest that the mental health of both fathers and mothers is important for the behavior of their children.