The prognostic significance of a histologic grading system was studied by an analysis of pathological specimens from 73 patients with ovarian epithelial cancers and tumors of borderline malignancies (tumors of low malignant potential) collected over a period of 25 years. The survival probability of patients in each group was analyzed by a computer program based on the product limit of Kaplan and Meier. The histologic grading scheme based on the presence of papillary formations or glands versus the presence of solid tumor nests proved to be prognostically significant for patients with stage I and II disease. The other grading system, based on cytologic features, was able to stratify survival rates into three instead of two groups distinguished by the histologic grading system. The survival of patients with moderately and poorly differentiated tumors was essentially the same. No difference was found between the prognoses of patients with cytologic grades 3 and 4.