Stage IIIA endometrial cancer includes patients with serosal or adnexal invasion and patients with positive peritoneal cytology only. In this study, we assessed the impact of peritoneal cytology on endometrial cancer survival. All endometrial cancer patients receiving surgery and radiotherapy at the Geneva University Hospitals between 1980 and 1993 were included. Stage IIIA cancers were categorised into 'cytological' stage IIIA (only positive peritoneal cytology) and 'histological' stage IIIA (serosal or adnexal infiltration). Survival rates were analysed by Kaplan-Meier method and compared using log-rank test. The prognostic importance of peritoneal cytology was analysed by multivariate regression analysis. This study included 170 endometrial cancers (112 stage I, 17 cytological stage IIIA, 18 histological stage IIIA, 9 stage IIIB+). Disease-specific survival of cytological stage IIIA was not different from stage I (94 vs 88% respectively, P=0.5) but better than histological stage IIIA (94 vs 51% respectively, P<0.01). Histological stage IIIA patients were at increased risk to die from cancer compared to stage I patients (HR 2.7, 95% CI 1.0-7.7), while cytological stage IIIA patients were not (HR 0.3, 95% CI 0.3-2.0). Cytological stage IIIA endometrial cancer has similar prognosis as stage l and better prognosis than histological stage IIIA. Additional research, definitively separating stage and cytology is warranted.