A three-wave longitudinal study design with two 6-month intervals was used to examine the stability and change in Internalizing, Externalizing, and Total Problem behavior among children and adolescents referred to outpatient mental health services. Our results indicated high stabilities for parent ratings of child psychopathology across a 1-year interval. Additionally, we found decreases in the level of problem behavior. Interindividual differences in change were found for Total Problems and Externalizing behavior but not for Internalizing. While both the child's temperament and intelligence level and family relations were related to the initial level of parent-rated problem behavior, only intermediary stressful life events had an influence on the rate of change of child psychopathology.