This study presents the results of a new surgical technique, resection of the medial end of the clavicle and interposition of the sternal head of the sternocleidomastoid muscle, that was used for the treatment of 17 painful sternoclavicular (SC) joints, 14 of which were available for review. The etiology of the pain was primary or posttraumatic degenerative arthritis in 10, osteitis condensans in 2, and SC joint infection in 2. The results of surgery, evaluated with the Rockwood SC joint rating scale and examination of the patients, were determined at a mean follow-up of 46 months. Results were excellent in 4 shoulders, good in 6, fair in 3, and poor in 1. All of the fair and poor results occurred in workers' compensation patients. Interposition arthroplasty performed in conjunction with resection of the medial clavicle proved to be a safe and effective method of treatment for the painful, degenerative or septic SC joint.