Few flow cytometric DNA analyses have used sufficient normal tissues and benign tumors as controls. To establish a basis for the interpretation of DNA flow cytometric results of gynecologic neoplasms, paraffin blocks from 121 patients with a diagnosis of serous cystadenoma (n = 37), mucinous cystadenoma (n = 28), leiomyoma (n = 41), and fibrothecoma (n = 15), and normal tissue samples obtained from some of these patients, including ovary (n = 20), cervix (n = 20), and myometrium (n = 20) were analyzed for nuclear DNA content. Absence of DNA aneuploidy was confirmed in all the normal tissues analyzed. Three (7.3%) of the leiomyomas, three (10.7%) of the mucinous cystadenomas, and one (6.7%) of the fibrothecomas were DNA aneuploid, whereas no unequivocal aneuploidy was found in the serous cystadenomas. The DNA indices of the aneuploid peaks varied between 1.10 and 1.97. The frequency of aneuploidy was related to tumor size in leiomyoma (p < 0.05). Prominent myxoid degeneration was noted in two of the three aneuploid leiomyomas. One of the three aneuploid mucinous tumors had focal cellular atypia and increased mitotic activity, and another had prominent papillary infoldings, focal breakdown of cyst walls, and rupture of mucin into the ovarian stroma. There was no progression or recurrence in those patients who had histologically benign but DNA aneuploid tumors during a mean follow-up of 58.1 months.