Lesions of the biceps pulley and the rotator cuff have been reported to be associated with an internal anterosuperior impingement (ASI) of the shoulder. The purpose of this study was to determine the factors influencing the development of an ASI. Eighty-nine patients with an arthroscopically diagnosed pulley lesion were prospectively included in this study. Four patterns of intraarticular lesions could be identified. Twenty-six patients (group 1) showed an isolated lesion of the superior glenohumeral ligament (SGHL). In 21 patients (group 2) an SGHL lesion and a partial articular-side supraspinatus tendon tear were found. Twenty-two patients (group 3) had an SGHL lesion and a deep surface tear of the subscapularis tendon, and in twenty patients (group 4) a lesion of the SGHL combined with a partial articular-side supraspinatus and subscapularis tendon tear was diagnosed. Of the patients, 80 (89.9%) showed involvement of the long head of the biceps tendon including synovitis, subluxation, dislocation, and partial or complete tearing. In 43.8% of all patients, ASI was observed. Whereas ASI was seen in 26.6% and 19.1% of patients in groups 1 and 2, respectively, 59.1% of patients in group 3 and 75% of patients in group 4 were found to have an ASI. ASI was significantly more often seen in patients with additional partial articular-side subscapularis tendon tears (P <.0001). In patients with acromioclavicular (AC) arthritis, ASI (62.5%) was more frequently observed than in patients without AC arthritis (P =.0309). In the multivariate analysis the stepwise selection procedure revealed only AC arthritis and the deep surface tear of the subscapularis (groups 3 and 4) to be significant influencing factors for an ASI. Our findings indicate that a progressive lesion of the pulley system, including partial tears of the subscapularis and supraspinatus tendons, contributes significantly to the development of an ASI. A pulley lesion leads to instability of the long head of the biceps tendon, causing increased passive anterior translation and upward migration of the humeral head, resulting in an ASI. In addition, a partial articular-side subscapularis and supraspinatus tendon tear reinforces the ASI.