Patients with malignant ovarian (n = 111) and borderline (n = 8) tumors (FIGO stage III/IV) underwent surgery and chemotherapy and were analyzed clinically (age, residual tumor after surgery) and morphologically (type, grade, psammoma body content), and by means of flow cytometry (DNA ploidy, S-phase fraction). Follow-up was 12-72 months for investigation of survival. Patients under 60 years of age (n = 18) with malignant tumors showed longer survival than patients over 60 (n = 93) (P = 0.078). Residual tumor was relevant for prognosis in malignant tumors only if macroscopically there was no residual disease (n = 13). There were no significant differences between residual tumors less than or equal to 2 cm (n = 61) and greater than 2 cm (n = 37). WHO typing was of little importance for survival analysis. Compared to borderline tumors (n = 8), serous (n = 65), endometrioid (n = 13), nonclassifiable (n = 12), mucinous carcinomas (n = 8), and nonepithelial tumors (n = 12) had a poor prognosis. Psammoma bodies were found in 25 patients with serous carcinomas, 7 of them had a high content. The prognosis for these 7 patients was much better than that for patients with a moderate or low psammoma body content (P = 0.006). Twenty-three epithelial tumors were graded G1, 28 were G2, and 47 were G3. However, grading was considered only as a prognostic factor in serous carcinomas (n = 65) (P = 0.028). A total of 199 DNA histograms from 119 patients were analyzed by flow cytometry (FCM). There were no correlations between tumor type and DNA ploidy or S-phase fraction. Seven of eight borderline tumor and all serous carcinomas with a high content of psammoma bodies were diploid combined with a low (less than or equal to 4%) S-phase fraction. DNA ploidy and S-phase fraction were excellent prognosticators. Of 99 epithelial malignant tumors, 35 were diploid and 64 were aneuploid. An S-phase fraction less than or equal to 4% was found in 39 patients, 4.1-10% in 73 patients, and greater than 10% in 23 patients. Diploid tumors and tumors with a low S-phase fraction showed the best survival (P = 0.007, resp. 0.0001). Our study emphasizes the importance of an accurate histology, including information on psammoma body content, and the importance of DNA flow cytometry. The advantage of FCM is that the results are simple, reproducible, and objective.