The goal of this study was to prospectively compare the early clinical results of intra-articular injection of hyaluronate or corticosteroid in patients with idiopathic adhesive capsulitis. The authors' hypothesis was that there would be no difference between groups. Sixty-eight patients with idiopathic adhesive capsulitis were equally randomized to receive either corticosteroid or hyaluronate injection. All patients underwent standard physical examination and magnetic resonance imaging. Intra-articular injection was performed through an anterior approach by the same orthopedic surgeon without image guidance. Patients were followed up 2 and 12 weeks after completion of the injection. The primary outcome was the Constant score at week 12. Secondary outcomes included the visual analog scale (VAS) pain score, the American Shoulder and Elbow Surgeons (ASES) score, and range of motion at each time point. No significant differences were noted in preoperative demographic features or baseline shoulder function between groups. After treatment, no significant differences were noted in early clinical outcomes (at weeks 2 and 12) with VAS, ASES, and Constant scores between groups (all P>.05). Evaluation of range of motion showed no difference in forward elevation or external rotation at each time point. Internal rotation was significantly lower at week 2 in the hyaluronate group compared with the corticosteroid group (P=.015). Internal rotation improved at week 12, with no significant difference between groups. Patients treated with intra-articular injection of hyaluronate and corticosteroid for idiopathic adhesive capsulitis showed significant improvement in early clinical scores and range of motion without significant differences between groups.