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A series of 30 myxofibrosarcomas is described. These malignant soft tissue tumours are characterized by a mucoid and nodular appearance, a coarse plexiform capillary pattern, and they are mostly seen subcutaneously (26 out of 30) in the extremities (24 out of 30) and trunk (4 out of 30) elderly people. Histochemical studies, comprising staining with Alcian blue and toluidine blue at different pH's with and without preceding digestion with testicular hyaluronidase and with the Scott technique, indicated the presence of hyaluronic acid but not sulphated glycosaminoglycans as chondroitinsulphates. Myxofibrosarcoma is believed to belong to the general category of fibroblastic and histiocytic malignant soft tissue tumours. The median diameter of the tumours was 7 cm. They were divided into 4 grades according to cellularity, cell atypia and mitotic activity. The grade III and IV tumours showed pronounced atypia, often with the bi- and multinucleated giant tumour cells and occasionally with giant cells of Touton's type, suggesting a relationship to malignant fibroxanthoma. All of the patients were treated surgically and one received also pre- and post-operative irradiation. None of the 2 grade I myxofibrosarcomas recurred, while 2 out of 7 grade II tumours, 6 out of 10 grade III tumours, and 7 out of 11 grade IV tumours recurred once and up to 9 times. Metastasis appeared in 7 out of 30 patients; grade I tumours were not seen in any of these cases. By the time of follow-up after intervals ranging from 1 month up to 27 years, 14 patients had died; 6 of these had died post-operatively or of intercurrent disease. The differential diagnosis between myxofibrosarcoma and other myxoid soft tissue tumours is discussed.