We prospectively studied extracorporeal shock wave therapy (ESWT) for calcific tendinitis of the shoulder in 46 consecutive patients. All patients were randomly divided into 2 groups: treatment and control. The 33 patients in the treatment group received 2 courses of ESWT at the energy density of 0.55 mJ/mm2 (1000 impulses). The control group underwent sham treatment with a dummy electrode (13 patients). Evaluation included the Constant score, pain scale, and radiographs. The ESWT results were good to excellent in 87.9% of shoulders (29/33) and fair in 12.1% (4/33), and the control results were fair in 69.2% (9/13) and poor in 30.1% (4/13). Among ESWT patients, calcium deposits were completely eliminated in 7 cases (21.2%), partially eliminated in 11 (36.3%), and unchanged in 15 (45.4%). In contrast, elimination was partial in 2 control patients (15.3%) and unchanged in 11 (84.7%). There was no significant difference between Ga ̈rtner type I and type II groups in the Constant score ( P >.05). ESWT shows promise for pain relief and functional restoration of calcific tendinitis with negligible complications. (J Shoulder Elbow Surg 2008;17:55-59.)