While uterine papillary serous carcinoma (UPSC) has been well described as a virulent subtype of endometrial adenocarcinoma (AC), with behavior similar to that of papillary serous ovarian carcinoma, the papillary endometrial (PE) variant has not been well characterized. We studied 117 patients with endometrial carcinoma identified by our tumor registry, pathology files, and practice records from March 1981 to February 1989: 76 with AC, 26 with PE, and 15 with UPSC. Age and demographic data were similar for all three groups. All of the AC patients, 84% of PE patients, and 87% of UPSC patients had early-stage disease by clinical exam; however, 10% of AC patients, 23% of PE patients, and 87% of UPSC patients had extrauterine disease at surgery (P less than 0.05). Deep myometrial invasion occurred in 29% of AC patients, 36% of PE patients, and 60% of UPSC patients (P less than 0.05). Comparative analysis of the PE and UPSC groups revealed more marked nuclear anaplasia (P less than 0.05) and more frequent vascular space involvement (nonsignificant) in the UPSC group. At 3 years, 75% of the AC group was alive without disease. In contrast, the median progression-free interval for the PE group was 33 months, and for the UPSC group, 9 months (P less than 0.05). These data suggest a transition of increasing virulence corresponding with increasing papillary features, from AC to PE to UPSC. The papillary feature may be a new, significant risk factor in endometrial carcinoma.