Hypertrophic osteoarthropathy is characterized by clubbing and periosteal new bone formation along the shaft of the long bones of the extremities. Although various intrathoracic malignancies have been associated with the development of HOA, it has been extremely rare for HOA to occur in a patient with a thymic carcinoma. Recently, we experienced a 63-year-old woman diagnosed as a thymic carcinoma with hypertrophic osteoarthropathy. She had both digital clubbing and cortical thickening in her lower extremities identified radiologically. We herein describe this case with a review of the literature.