Eighteen carcinomas involving both the endometrium and the ovary were studied. Stage, size, bilaterality and pattern of ovarian involvement, histologic types and grades, presence of endometrial hyperplasia or ovarian endometriosis, myometrial, tubal, lymphatic and blood vessel invasion, and follow-up of the patients were all evaluated. Accordingly, the cases were classified as follows: Group A (nine cases), two separate primary tumors; and Group B (nine cases), uterine primaries with ovarian metastasis or ovarian primaries with uterine metastasis. Immunohistochemical stains (CAM 5.2, wide-spectrum keratin, vimentin, carcinoembryonic antigen (CEA), CA 12.5, CA 19.9) were performed in all cases. Flow cytometric determination of nuclear DNA was done in 13 (seven Group A and six Group B tumors). Of the nine cases with independent primary tumors, seven showed different immunohistochemical profiles in the ovarian and uterine tumors, whereas only four of the nine metastatic ones had similar staining characteristics. Five cases with independent primary tumors, but only one of the metastatic group, exhibited different aneuploid stemlines in the endometrial and ovarian tumors. The other seven (two independent and five metastatic) cases had similar DNA indexes in both tumors. Immunohistochemical and DNA flow cytometric study may be of some value for the distinction between metastatic and independent tumors, but differential diagnosis must presently rely largely upon conventional clinicopathologic criteria.