Giant cell tumor of the tendon sheath (also known as “giant cell synovial tumor”, “limited nodular tenosynovitis” and “pigmented villous nodular synovitis”) is the second most common mass in the hand (the most common being a tendon sheath cyst). It is the second most common swelling of the hand (the most common is the tendon sheath cyst) and was first described by Chassaignac in 1852 as a benign soft tissue mass that is tough, fixed, and slow growing, usually 1-3 cm in diameter, often attached to the tendons of the fingers and wrists, and more commonly to the flexor tendons of the wrists, but also to the toes, ankles, and knees, etc. It is prevalent between 20 and 50 years of age. It is usually painless and may lead to osteo-cortical erosion. As with most soft tissue tumors, the etiology of tenosynovial giant cell tumors is unknown. Theories of etiology include trauma, abnormal lipid metabolism, osteoblast proliferation, infection, vascular disorders, immune mechanisms, inflammation, and metabolic disorders. The most widely accepted theory is the proliferation associated with an inflammatory process according to Jaffe et al. The clinical differential diagnosis includes foreign body granuloma, necrotizing granuloma, tenosynovial fibroma, infection, tenosynovial cyst, rheumatoid nodule, epidermoid cyst, lipoma, and other less common solid tumors. It is relatively easy to rule out these lesions after a detailed history and physical examination. Complete surgical removal of the tumor is the best treatment, but the tumor is prone to recurrence, with a recurrence rate of 4-45%. Recurrent recurrence can be combined with radiation therapy.