A case of unilateral, subscapular elastofibroma dorsi secondary to degenerative osteoarthritis in the ipsilateral glenohumeral joint is presented. A 69-year-old woman had experienced symptoms of osteoarthritis in the right shoulder since contracting septic arthritis when she was 7 years old. The patient noticed a soft tissue mass in the right subscapular region when she was 65 years old. The range of motion of the glenohumeral joint was severely restricted. Histopathologic examination of the excised mass revealed elastofibroma. The authors think the excessive scapulothoracic motion was important in formation of the lesion. This case indicates that elastofibroma is not a true neoplasm but a reactive lesion formed by repetitive minor trauma.