Increasingly more research is showing that stress has an influence on the development and maintenance of externalizing problem behavior in adolescents. Stress, for example, causes more impulsivity and limits emotion regulation. Mindfulness focuses on stress reduction and therefore appears to be a (supportive) treatment option with added value for adolescents with externalizing problem behavior. A multilevel meta-analysis (14 studies and 48 effect sizes) was conducted to gain more insight into the effectiveness of this treatment form in reducing externalizing problem behavior. It specifically considered whether the involvement of parents or other combined forms of treatment influenced the effect. The results showed that mindfulness-based interventions are effective in reducing externalizing problem behavior in adolescents, with a large effect size (d = 0.99). The effect was found to be even greater (d = 1.14) after correction for selection bias. The moderator analysis revealed that none of the variables examined had an impact on the effect of mindfulness-based interventions. The results of the moderator analysis should be interpreted with caution. Due to the fact that parents were not involved intensely enough, were barely motivated, and no follow-up data are known about the effectiveness.