• Giant cell tumor of the tendon sheath is the second most common tumor of the fingers and hands but is only rarely mentioned in the dermatologic literature. Although its pathogenesis has been debated, it is probably a type of fibrous histiocytoma. This tumor is almost always benign but may locally invade the overlying dermis and be confused with a malignant neoplasm. It often extends to the synovium of the adjacent joint space and necessitates total excision to prevent local recurrence. Therefore, excision should be undertaken by a physician who is surgically qualified for such procedure. We report a case that illustrates the clinical and pathologic aspects of this lesion. (Arch Dermatol114:944-946, 1978)