Giant cell tumor of the tendon sheath(GCTTS) is a benign condition which involves the synovium of the tendonsheaths, and usually occurs around the small joints, e. g. the ankle, knee, and wrist. Histologically, GCTTS is similar to pigmented villonodular synovitis(PVNS). The authors report MRI findings of a GCTTS. This showed lower signal-intensity lesions than adjacent muscles on T1-weighted, proton density weighted, and T2-weighted images.