Objective: This study evaluates the longitudinal outcomes of Families OverComing Under Stress (FOCUS), a family-centered preventive intervention implemented to enhance resilience and to reduce psychological health risk in military families and children who have high levels of stress related to parental wartime military service. Method: We performed a secondary analysis of evaluation data from a large-scale service implementation of the FOCUS intervention collected between July 2008 and December 2013 at 15 military installations in the United States and Japan. We present data for 2,615 unique families (3,499 parents and 3,810 children) with completed intake and at least 1 postintervention assessment. Longitudinal regression models with family-level random effects were used to assess the patterns of change in child and parent (civilian and military) psychological health outcomes over time. Results: Improvement in psychological health outcomes occurred in both service member and civilian parents. Relative to intake, parental anxiety and depression symptoms were significantly reduced postintervention, and these reductions were maintained at 2 subsequent follow-up assessments. In addition, we identified an improvement over time in emotional and behavioral symptoms and in prosocial behaviors for both boys and girls. We observed reductions in the prevalence of unhealthy family functioning and child anxiety symptoms, as well as parental depression, anxiety, and posttraumatic stress symptoms from intake to follow-up. Conclusion: Longitudinal program evaluation data show sustained trajectories of reduced psychological health risk symptoms and improved indices of resilience in children, civilian, and active duty military parents participating in a strength-based, family-centered preventive intervention.