PURPOSE: We wanted to determine if preoperative three dimensional (3D) ultrasonographic evaluation for rotator cuff tear is useful to measure the real size of a torn rotator cuff for performing an operation MATERIALS AND METHODS: This study included 15 cases (7 males and 8 female), and these patients were confirmed to have a full thickness tear of the rotator cuff by 3D ultrasonography and the operative findings, as well as on the magnetic resonance imaging (MRI). The average age of the patients was 55.4yrs. RESULTS: The average difference between the 3D ultrasonographic and operative measurements of the full thickness tear of the rotator cuff was 0.7 mm in the transverse length and 2.0 mm in the longitudinal length. CONCLUSION: The low error between the 3D ultrasonographic and intraoperative measurements of rotator cuff tear shows the usefulness of preoperative 3D ultrasonographic evaluation for rotator cuff tear.