This report consists of 2 parts. Part I: The usefulness of computed tomography (CT) in the diagnosis of rotator cuff tear was assessed. The rotator cuff could not be visualized in detail by CT unless introduction of contrast material into the joint cavity was performed. CT arthrography was performed on 21 cases of rotator cuff tears. The most detailed information was obtained when a relatively low concentration of contrast material (3.25% Angiografin) was filled in the joint cavity, and when the shoulder joint was rotated to the maximum outwards at the side. CT arthrography proved to be the most reliable method for assessing the extent and portion of the rotator cuff tears, so that it demonstrated conclusive evidence of diagnosis and management in 89% of patients studied. Part II: The usefulness of CT in the diagnosis of bone and soft tissue tumors was assessed. CT examination provided unique preoperative information which could imagine a more precise histological characteristics and anatomical localization of the lesion. Contrast enhancement (CE), when used, proved to be helpful in predicting the nature of tumors. The CE by intra-arterial infusion, or intravenous bolus injection of contrast material during the scan was more useful than that by intravenous drip infusion of the material. The information regarding change of tumor size, CT number and CE were appropriate indicators which directly corresponded to responsiveness of the tumor to the chemotherapy and radiotherapy performed. Preoperative ABC classification of the tumor by information regarding its size, location, definition and anatomical relation of tumors to vital structures (neural, vascular, and visceral) was done by using CT. The classification clearly corresponded to the status of patients regarding the treatment required for the patients.