We report a case of thymic carcinoma presenting as unilateral shoulder pain for 13 months. Before an accurate diagnosis was made, the patient received conservative treatment, cervical discectomies, and myofascial trigger point injection, none of which relieved his pain. When thymic carcinoma was eventually diagnosed, he received total resection of the tumor and the shoulder pain subsided completely. Thymic carcinoma is a rare carcinoma, and our review of the literature did not show shoulder pain as its initial presentation except for one case report. The purpose of this report is to document our clinical experience so that other physiatrists can include thymic carcinoma in their differential diagnosis of shoulder pain.