Previous studies of the relationship between temperament and psychopathology have been limited by focusing on main effects of temperament on psychopathology, reliance solely on maternal reports of child temperament, and predominately using cross-sectional designs. This study extended this work by focusing on interactions between reactive (positive emotionality/PE; negative emotionality/NE) and regulatory (effortful control) dimensions of temperament, using laboratory observations of temperament, and focusing on longitudinal prediction of internalizing and externalizing behavior problems. 536 children (46.1% Female, 92.4% White) were followed in a prospective, longitudinal study of the relationship between temperament and psychopathology. Temperament was assessed using laboratory observations when children were at age 3. Mothers and fathers reported on internalizing and externalizing symptoms in their children at ages 3, 6, and 9. Multilevel modeling analyses examined associations between the interaction of temperament traits and patterns of change in internalizing and externalizing psychopathology. Interactions between reactive PE traits (Sociability, Exuberance), but not NE traits (Dysphoria, Fear), and regulatory temperament (Disinhibition) were associated with the slope of maternal-reported internalizing and paternal-reported externalizing symptoms such that youth low in PE traits and high in effortful control experienced a greater decline in symptoms over time. In conclusion, among children with lower levels of PE traits, strong regulatory abilities are associated with greater reductions in internalizing and externalizing symptoms over time. These models highlight the complex interaction between reactive and regulatory temperament and expand current understanding of temperamental risk for psychopathology.