Pseudomyxoma peritonei is a clinical entity that has lead to much confusion about its etiology, clinical manifestations, treatment, and prognosis. Pseudomyxoma peritonei is currently defined as a grade I mucinous adenocarcinoma that arises from a primary appendiceal adenoma. The clinical entity is defined by a redistribution phenomenon. This means that cancer cells from the appendix tumor are found localized at predetermined sites within the abdomen and pelvis but that the primary tumor may be small and inconspicuous. The small bowel is spared of mucinous tumor, while spaces beneath the hemidiaphragms and within the pelvis are filled by disease. The omentum is massively replaced by tumor in most patients. The disease, when treated by multiple surgical procedures, presents a median survival of approximately 2 years. Good results depend on early diagnosis and treatment before large volumes of disease and multiple surgical procedures lead to small bowel entrapment by tumor. In modern therapy using peritoneotomy procedures and intraperitoneal chemotherapy with mitomycin C and 5-fluorouracil, the long-term survival at 10 years approaches 80 percent.