Objective: Mental illness in parents affects the mental health of their children. A systematic review and a meta-analysis of the effectiveness of interventions to prevent mental disorders or psychological symptoms in the offspring were performed. Method: The Cochrane, MEDLINE, EMBASE, and PsycINFO databases were searched for randomized controlled trials of interventions in parents with mental disorders. Outcomes in the child included incident mental disorders of the same nature and internalizing (negative emotions, depressive symptoms, anxiety) or externalizing (hyperactivity, aggressiveness, behavioral problems) symptoms. Relative risks and standardized mean differences in symptom scores were combined in random-effects meta-analysis. Results: Thirteen trials including 1,490 children were analyzed. Interventions included cognitive, behavioral, or psychoeducational components. Seven trials assessed the incidence of mental disorders and seven trials assessed symptoms. In total 161 new diagnoses of mental illness were recorded, with interventions decreasing the risk by 40% (combined relative risk 0.60, 95% CI 0.45-0.79). Symptom scores were lower in the intervention groups: standardized mean differences were -0.22 (95% CI -0.37 to -0.08) for internalizing symptoms (p = 0.003) and -0.16 (95% confidence interval -0.36 to 0.04) for externalizing symptoms (p = 0.12). Conclusions: Interventions to prevent mental disorders and psychological symptoms in the offspring of parents with mental disorders appear to be effective. (Contains 4 figures and 3 tables.)