Malignant mixed mesodermal tumors of the ovary occur in less than 1% of cases of ovarian cancer. They have a dismal prognosis and the most effective type of therapy is still not known. All cases of malignant mixed mesodermal tumor of the ovary between January 1, 1985 and May 1, 1994 operated on by the gynecologic oncology service are the subject of this report. Data were obtained from the hospital and office records of the patients. Nine patients who had their primary surgery by the gynecologic oncology service were found to have the diagnosis of malignant mixed mesodermal tumor of the ovary. Homologous tumors were found in five patients and heterologous tumors in four. Homologous tumors (mean survival 15.2 months) showed a better survival than heterologous tumors (mean survival 6.5 months; P = 0.001). An elevated estrogen receptor status was shown to correspond to longer survival (P < 0.0001). Six specimens were considered to be estrogen receptor positive and three were receptor negative. The mean survival in those patients who had a positive estrogen receptor status, 13.7 months, with a median of 7.5 months was significantly higher than those who were not positive, 6.7 months (P = 0.019) with a median of 6.25 months. All specimens were progesterone receptor negative. Malignant mixed mesodermal tumors of the ovary have a dismal prognosis, no effective therapy, and controversial prognostic indicators. Increasing estrogen receptor status appeared to correlate with longer mean survival. Larger, multi-institutional studies need to be done to determine the overall significance of these findings.