This is a study of 12 cases of Stage III ovarian serous neoplasms of low malignant potential associated with focal areas (< 50%) of serous carcinoma. The purpose of this study was to assess the prognosis of serous tumors that had areas of serous carcinoma but were predominantly of low malignant potential. Eleven serous carcinomas were low grade, and one was high grade. All of the patients underwent surgical resection of the neoplasm and then chemotherapy. Eight patients died of disease after a follow-up of 17 to 94 months (mean, 52 mo). Three patients had no evidence of disease at 60, 69, and 75 months. One patient is alive with progressive disease at 58 months. Serous neoplasms of low malignant potential associated with focal areas (< 50%) of serous carcinoma are aggressive neoplasms that have a prognosis similar to that of serous carcinoma.