In an open, uncontrolled trial, the clinical and radiological responses to calcitonin therapy in the treatment of acute calcifying tendinitis of the shoulder were investigated. A total of 35 patients (38 shoulders) were enrolled. Each patient was injected with 10 U synthetic calcitonin intramuscularly twice a week. The mean number of injections was 6.0 (range, 1–16). At the end of the treatment period, 33 shoulders (87%) were pain-free. In 28 shoulders (74%), the localized pain disappeared within 2 weeks of the start of treatment. In 25 shoulders (66%), the clinical results were rated as good, with complete pain relief and sufficient recovery in the activities of daily living (ADL) and active range of shoulder joint motion (ROM). On the contrary, in 4 shoulders (10%) pain persisted, requiring alternative treatment. In 28 shoulders (74%), the pre-existing calcific deposits were remarkably reduced or had disappeared. Radiologically, the shoulders with fluffy-type deposits had greater pain relief and ROM recovery than those with defined-type deposits. However, there was no correlation between the clinical results and localized region or size of deposits. In 19 cases (50%) where the calcified deposits had completely disappeared, the shoulder had become pain-free, and in all of them except two cases there was complete recovery of ROM. No patient developed clinical complications. These results suggest that calcitonin treatment may be useful for calcifying tendinitis of the shoulder, and that this therapy results in both clinical and radiological improvement in this condition.