Forty-one patients with epithelial malignancies of the ovary treated at the Medical College of Wisconsin Affiliated Hospitals from 1976 to 1984 had paraffin embedded tissue available for review. Of the 41 patients, 40 had adequate material to provide 50 micron sections that were evaluated with flow cytometry to determine DNA content. Tumor- and patient-related parameters were then correlated with the results of flow cytometry. Overall survival at 5 years in these patients was 43%, and relapse-free survival was 50%. Forty percent of the tumors were diploid, and 60% were aneuploid. Five-year survival for diploid patients was 74% with a relapse-free survival of 71%. Corresponding overall and relapse-free survivals for aneuploid patients were 22% and 35%, respectively. Distribution of the patients by histology, stage, and grade was equal between the diploid and aneuploid groups. All patients were treated with whole abdominal plus concomitant pelvic boost irradiation; total doses to the whole abdomen ranged from 10 Gy to 46 Gy (1000 to 4600 cGy) with the median dose being 37.5 Gy. Approximately 40% of the patients received chemotherapy, which usually consisted of a single agent (Alkeran, Burroughs Welcome, Research Triangle Park, NC). This retrospective study of patients with ovarian cancer treated with radiation therapy suggests the possibility that determinations of DNA ploidy may be useful in selecting patients whose poor prognosis dictates that a more aggressive therapy be used.