During a 8-year period, recurrent swelling of the right knee-joint was observed in a 31-year-old female. Although only minimal pain was present, flexion of the knee-joint was severely limited. Bearing in mind the extent of the swelling, the initial diagnostic procedures were suggestive of a malignant neoplasm. Biopsy of the knee-joint led however to the diagnosis of a pigmented villo-nodular synovitis. The postoperative course after synovectomy of the knee-joint was uneventful. Although benign, this lesion has to be followed-up closely, due to the recurrence-rate of 33%.