This study examined the effects of high-energy shock wave treatment on the course of calcifying tendinitis of the shoulder. Twenty patients were included in the protocol. Shock waves were applied to the calcifications with a lithotripter in two sessions of 2000 pulses each. The energy that produced the shock wave was 18 to 22 kV. Six and 12 weeks after treatment the subjective and functional state was assessed with the Constant score. All patients underwent radiographs and magnetic resonance imaging. At the 12-week follow-up evaluation 15 patients had a marked reduction of symptoms with an average of 30% improvement in the Constant score. Radiographs showed a complete elimination of the calcifications in seven patients, and in five cases a partial disintegration was seen. The overall morbidity was low; 14 patients had a transient subcutaneous hematoma. Magnetic resonance imaging did not show any lasting damage to bone or soft tissue.