[en] In summary, a 43-year-old man presented with pain and swelling around the left knee. Radiological studies at the time of the present admission showed the typical stigmata of an osteosarcoma in the distal segment of the femur. Thirteen years previously the lesion at the distal end of the same femur had been curetted. The lesion initially was called a benign fibro-osseous tumor - or fibroxanthoma. On the admission 13 years later in 1983 the tumor had grown perceptibly with tumor bone extending into the soft tissues, giving the typical appearance of an osteosarcoma. The leg was amputated and the histological sections showed the typical stigmata of an intramedullary, central osteosarcoma (of a low-grade-well differentiate type). (orig./SHA)