In pseudomyxoma peritonei a mucinous tumor of the appendix spreads into the abdominal cavity. Cytologic picture of the tumor may be benign, malignant or intermediary. The symptoms were previously relieved by repeated resections of the tumor mass, whereby even the most benign form of the disease progressed slowly. A method has now emerged in which radical-aimed surgery is combined with intraperitoneal lavage with a warmed solution of a cytotoxic agent. This treatment is associated with a morbidity of 33 to 56% and a mortality of 0 to 18%. Controlled studies have not been carried out on the novel treatment.