Rotator cuff tear secondary to chronic synovitis eroding the rotator cuff tendon is a complication of rheumatoid arthritis that has received little attention. Patients with such tears have a long history of active rheumatoid disease preceding the sudden onset of increased unilateral shoulder pain and immobility. The physician may interpret this change as indicating a joint infection or rheumatoid flare, and initiate a drastic change in the patient's therapy. Shoulder arthrography reveals the correct diagnosis. Appropriate treatment consists of heat, rest, range of motion exercises, and repeated intra-articular injection of steroids.