Anxiety and depression are highly comorbid and share several common etiological processes. Therefore, it may be more efficient to develop interventions that treat or prevent these problems together rather than as separate entities. The present meta-analytic review examined whether interventions for children and adolescents that explicitly targeted either anxiety or depression showed treatment specificity or also impacted the other outcome (i.e. cross-over effects). We addressed this question both within the same type of study (i.e. treatment, prevention) and across study types. Only randomized controlled trials (RCTs) that assessed both constructs with dimensional measures were included in this review. For treatment studies, RCTs targeting anxiety (n = 18) showed significant effects on both anxious and depressive symptoms, although more strongly on anxiety than depression; similarly, RCTs treating depression (n = 9) yielded significant effectson both depressive and anxious symptoms, but stronger effects on depression than anxiety. Thus, there were cross-over effects in treatments purportedly targeting either anxiety or depression, and also treatment specificity, such that larger effects were seen for the target problem at which the treatment was aimed. Anxiety prevention studies (n = 14) significantly affected anxious, but not depressive symptoms, indicating no cross-over effect of anxiety prevention trials on depression.For depression prevention studies (n = 15), the effects were not significant for either depressive or anxiety symptoms, although the effect was significantly larger for depressive than for anxious symptoms. Post-hoc analyses revealed that the effect on depressive symptoms was significant in depression preventions trialsof targeted but not universal samples. Implications for transdiagnostic interventions are discussed.