Tumor ploidy was determined by flowcytometry (FCM) in paraffin-embedded tissue of 74 patients with advanced ovarian cancer (International Federation of Gynecology and Obstetrics [FIGO] 2B, 3, 4). Significant differences in survival and progression-free survival were found between classes of tumor ploidy as well as for several clinical parameters, including FIGO stage, histologic grade, diameter of the largest metastases, presence of ascites, peritoneal carcinomatosis, and size of residual tumor. In a Cox regression analysis, tumor ploidy and presence or absence of ascites were the only significant factors for survival, whereas ascites and residual tumor proved to be the significant parameters for progression-free survival. Tumor ploidy was strongly associated with tumor bulk, size of residual tumor, and histologic grade. Tumor ploidy was the same within different tumor sites in the majority of the cases. On the basis of these findings tumor ploidy is considered to be a major prognostic factor for survival in advanced ovarian cancer.