143 patients with symptomatic subacromial impingement were randomized to a supervised exercise program with the addition of either radial extracorporeal shockwave therapy (rESWT) or sham rESWT. Patients were assessed for outcome on the Shoulder Pain and Disability Index (SPADI), pain at rest, and pain during activity. In analysis of all patients, there were no significant between-group differences for any outcome measure. In the subgroup of patients with rotator cuff calcification, patients treated with rESWT demonstrated better scores for the SPADI and pain during activity when compared to patients who received sham rESWT,