Flow cytometric DNA-ploidy analysis of synchronously occurring multiple malignant tumors of the female genital tract. In this study the authors applied flow cytometric DNA-ploidy analysis to multiple female genital tract malignant tumors in 43 patients, most of whom (n = 37) had bilateral ovarian cancer. An algorithm was developed for calculation of the likelihood ratio of the probabilities that measured DNA index differences between multiple tumor localizations within the same patient could be attributed to measurement variation or to true biologic DNA content differences. The results of this statistical analysis show that in 72% of the cases (31 of 43) this probability ratio exceeded 1. Because the probability that two independent tumors will have a near-identical aneuploid DNA content is very low, this finding supports a metastatic process rather than the occurrence of multiple primary tumors in these patients. Thus, flow cytometric DNA-ploidy analysis can be helpful in the identification of metastatic disease in patients with multiple female genital tract malignant tumors. 