The case of a 55-year-old patient is described, presenting the clinical sign of a chronic infection of the tendon sheath. Upon incision a mass of brown synovial tumor was found. The X-ray showed a circumscript bone erosion. MRI demonstrated tumor involvement of all flexor tendons up to the forearm. Under radiation the tumor initially was diminished. Half a year later, pulmonary metastases were found. The destruction of the whole skeleton of the hand led to a forearm amputation. Later, a metastasis was found in the tongue. The patient died with the clinical signs of pulmonary insufficiency. Autopsy showed diffuse pulmonary metastases. This case is discussed together with other rare cases of malignant pigmented villonodular synovialitis arising from joints and tendon sheaths.