Music therapy is the therapeutic use of music and musical activities in the treatment of somatic and mental diseases. In the last decades it has developed from a quasi-professional working field into an increasingly evidence-based treatment for various diseases. Selected outcome studies that were carried out in order to give music therapy a scientific and empirical base are presented in this article. Results show that music therapy is an effective intervention for patients with chronic pain, children with migraine, and patients suffering from chronic tinnitus. This positive outcome, in combination with the observed moderate to large effect sizes in different metanalyses, provides evidence for the use of music therapy in specific clinical fields. Future research should focus on studies that compare well-defined music therapy interventions to standard treatment.