Background: Meta-analyses of youth mass trauma intervention studies have focused primarily on posttraumatic stress even though depression and anxiety are common maladaptive outcomes that require intervention. Objective: This meta-analysis examined youth mass trauma intervention effects on depression and anxiety relative to natural recovery and characteristics of the event, context, population, intervention, and intervention delivery that may have moderated these effects. Method: A literature search identified 21 studies investigating the effectiveness of 24 randomized controlled trials with inactive controls (21 trials examined depression and 8 examined anxiety; 5 examined both). Intervention effects were computed as Hedge's g estimates and combined using random effects models. Moderator analysis computed intervention effect sizes across selected covariates. Results: The summary intervention effect was not significant for either depression or anxiety. There were statistically significant effects for depression with interventions delivered following a natural disaster (g = 0.40; p = 0.0192) or in a high income country (g = 0.30; p = 0.0253) and with non-trauma-focused interventions (g = 0.29; p = 0.0155) and those delivered in more than eight sessions (g = 0.23; p = 0.0416). The effect for anxiety symptoms was significant only with non-trauma-focused interventions (g = 0.83; p = 0.0428). Conclusions: Given the prevalence of depression and anxiety post event, greater attention is warranted to develop and maximize the benefit of interventions for these outcomes. The findings suggest that trauma-focused interventions may need to be augmented with specific components directed at depression and/or anxiety.