Although several histopathological changes have been developed in frozen shoulder, frozen shoulder is mostly accompanied by the changes of the rotator cuff which has the most important function in movement and has a role in stabilizing the shoulder joint. The changes of the rotator cuff in frozen shoulder have not been reported in Korea yet, but Simon reported that there was an attenuation of the rotator cuff in frozn shoulder. Accordingly, we observed the changes of the rotator cuff in frozen shoulder by ultrasonography, which has no rsdiation exposure and is non-invasive. The authors practiced the shoulder ultrasonography on 36 patients with a pain and limitation of motion in shoulder at the Dept. of Orthopedic Surgery, Hangang Sacred Heart Hospital, Hallym University, from March in 1988 to August in 1988. The results are as follows ;1) Ultrasonography is thought to contribute a great deal in detection of the changes of the rotator cuff, especially of the thickness of the rotstor cuff. 2) Among 36 patients, the thickness of the rotator cuff of 35 patients was 6.494+1.008 mm (M+SD) in the affected shoulder and 6.475+1.052 mm(M+SD) in the unaffected shoulder. In only one pstient, the thickness of the rotator cuff was 1.68+0.58 mm(M+SD) in the affected shoulder and 553+1.16mm(M+SD) in the unaffected shoulder. Theres no significant change in the thickness of the rotator cuff measured by ultrasonography in frozen shoulder. 3) Ultrasonography is an excellent diagnostic method in detecting the rupture of the rotator cuff in frozen shoulder.