Background: Intra-articular corticosteroid injection is a common therapy for adhesive capsulitis, but there is a lack of prospective randomized controlled studies analyzing the efficacy of single injections applied blindly to accelerate improvement in pain and function. Hypothesis: In patients with adhesive capsulitis, a single intra-articular corticosteroid injection without image control applied before the beginning of a physical therapy program will accelerate pain relief and recovery of function compared with oral nonsteroidal anti-inflammatory drugs (NSAIDs) and physical therapy. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 74 patients with primary adhesive capsulitis in the freezing stage were randomized to receive either intra-articular injections with betamethasone or oral NSAIDs. Clinical outcome was documented at baseline and after 2, 4, 8, and 12 weeks and comprised a visual analog scale (VAS) for pain, the American Shoulder and Elbow Surgeons (ASES) Shoulder Score, the abbreviated Constant-Murley score, and the abbreviated Disabilities of the Arm, Shoulder and Hand (QuickDASH) score for function. Passive range of motion was measured with a goniometer. Results: Patients treated with corticosteroid injections achieved faster pain relief compared with control patients during the first 8 weeks after treatment ( P < .001). However, no significant difference in pain was observed among the groups at final follow-up. Likewise, shoulder function and motion improved significantly in both groups at all follow-up points. Shoulder function scores and most motion parameters improved faster in the injection group up to week 8 ( P < .001). Again, no significant differences in function or motion were seen at final follow-up. Conclusion: In patients with adhesive capsulitis, a single corticosteroid injection applied without image control provides faster pain relief and earlier improvement of shoulder function and motion compared with oral NSAIDs.