We studied 164 cases of Stage I endometrial adenocarcinoma to determine the relative prognostic value of International Federation of Gynecology and Obstetrics (FIGO) and nuclear grading systems. Other factors known to be of prognostic value in endometrial carcinoma also were evaluated. Both the FIGO and nuclear grading systems correlated with five-year mortality rate from cancer. Nuclear Grade 3 proved to be a superior predictor of fatal outcome (nine of 13 [69%] ) over FIGO Grade 3 (four of 13 [31%]). We advocate the combined use of FIGO and nuclear grading systems, along with other prognostic parameters, for the detection of most patients with fatal cancer.