The purpose of this study was to evaluate consecutive shoulder arthroscopies for the presence or absence of a space between the biceps tendon and the supraspinatus as an indicator of a full-thickness rotator cuff tear. We performed 588 consecutive shoulder arthroscopies in the lateral decubitus position, and the presence or absence of a space between the rotator cuff (supraspinatus) and the biceps tendon was recorded immediately upon entering and insufflating the joint. Of the 588 patients, 174 (30%) were found to have full-thickness rotator cuff tears. Of these 174 patients, 171 had absence of the space between the biceps and the supraspinatus, for a sensitivity of 98%. Of the 414 patients in whom no full-thickness tear was present, 4 had absence of the space, for a specificity of 99%. The 4 patients with a false-negative result had adhesive capsulitis. During shoulder arthroscopy, a normal interval exists between the supraspinatus and biceps tendons as a result of joint insufflation. Loss of this interval is both highly sensitive (98%) and specific (99%) for a full-thickness rotator cuff tear. The space between the rotator cuff and the biceps tendon can be a reliable adjunct for verification of a full-thickness rotator cuff tear immediately upon entering the shoulder joint but should not be used in place of a full arthroscopic evaluation of the cuff.