97 patients with symptomatic primary adhesive capsulitis for less than 9 months were included in this trial to compare the efficacy of three sites for corticosteroid injections. Patients were randomized to receive an injection of 1mL 40mg/mL triamcinolone acetonide with 2mL 2% lidocaine within the rotator interval along the coracohumeral ligament, in the intraarticular space, or in the subacromial space. All injections were performed under ultrasound guidance. At 12 weeks, pain, passive flexion, abduction, external rotation and internal rotation, Constant score, and DASH score were significantly better in the rotator interval group compared to the two injection site groups.