The aim of this meta-analysis was to evaluate the effectiveness of psychoeducational interventions in reducing stress and to gain more insight in determining features moderating the magnitude of effects. Relevant studies were selected from 1990 to 2010 and were included according to predetermined criteria. For each study, the standardized mean difference was calculated for the outcome measure primarily related to stress. Nineteen studies met the inclusion criteria; for 16 studies, a standardized mean difference could be calculated. The average effect size was .27 (95% confidence interval = [.14, .40]) at posttest and .20 (95% confidence interval = [−.04, .43]) at follow-up. To determine possible moderators of intervention effects, all 19 studies were included. Only interventions that were shorter in duration provided better results. When a model with multiple moderators was considered, a model combining both intervention duration and the number of women in an intervention was significant and accounted for 42% of the variability found in the data set. Specifically, interventions with more women that were shorter in duration obtained better results.