Peritoneal adenocarcinoma (serous or other subtype) of Müllerian type (PAMT) is frequently misclassified as another primary tumor. Peritoneal carcinomatosis in women without evidence of a primary site may occur secondary to a number of processes. Confusion regarding the nomenclature has made it difficult to determine the incidence and natural history of this unique malignancy. Other terms used for this tumor include mesothelioma, peritoneal papillary serous carcinoma, extra-ovarian serous carcinoma, and normal-sized ovarian carcinoma syndrome. Thirty-four patients (33 serous and one endometrioid) were identified with PAMT during 1976 through 1988. One hundred and thirty-seven patients underwent primary cytoreductive surgery for a preoperative diagnosis consistent with ovarian cancer. Twenty-nine (21.2%) were classified as PAMT (5 of the 34 had their initial surgery at other institutions). The mean age was 61.4 years. The primary symptoms and signs were abdominal pain (68%) and ascites (52%). Twenty-five (73%) had a preoperative diagnosis of ovarian cancer while the postoperative diagnosis was unknown (44%), PAMT (29%), and ovarian cancer (27%). Univariate and multivariate survival analysis were performed. Survival was independent of age, residual disease, grade, ascites, type of chemotherapy, and second-look results. In patients with residual disease < 1.5 cm, extended survival was found in (hose with ascites < 1000 ml, residual disease in pelvis only, and small residual volume but statistical significance was not obtained. Twenty-eight patients received ≥4 courses of chemotherapy after primary surgery. Twelve of 21 patients (57%) who received cisplatin (CDDP) survived between 23 and 92 months, while no patient receiving other chemotherapeutic regimens survived more than 25 months. The 2 and 3 year survival rate for CDDP was 47% and 33% vs. 14% and 0% for other regimens. Optimal cytoreductive surgery was not an independent prognostic factor as found in ovarian cancer, probably secondary to unresectable peritoneal carcinomatosis. PAMT is sensitive to chemotherapy but only the use of CDDP was associated with long term survival. Based on these results, women with peritoneal carcinomatosis consistent with PAMT should receive a CDDP-based regimen after primary surgery.