In a prospective study of 283 women with endometrial carcinoma, 29 of whom were premenopausal and 254 postmenopausal, the DNA content and S-phase rate were measured by flow cytometry. Over 90% of the tumors in premenopausal women were peri-diploid and the remaining tumors were tetraploid, whereas 23% of the tumors in post-menopausal women were grossly aneuploid (p less than 0.01). Similar differences were found between women younger or older than 50 years. The results indicate that the hormonal status and/or age are of importance for the development of genetically different forms of endometrial carcinomas, as judged from the DNA-distribution.