Among the clinical parameters that play a pivotal role in predicting the outcome of patients with endometrial carcinoma, intraperitoneal microscopic dissemination represents an important cause of recurrences. To date, peritoneal cytology has been incorporated into the current surgical staging system (International Federation of Gynecology and Obstetrics 88), although its predictive value remains a controversial issue. In this study the authors investigated the possibility of applying immunocytochemistry (ICC) to the diagnosis of peritoneal washing (PW) aimed at improving conventional cytology and verifying the prognostic value of peritoneal malignant cells. The authors analyzed 182 PWs sampled from endometrial cancer patients. The ICC analysis was performed using two monoclonal antibodies (MAbs)--AR-3 and B72.3--that in combination recognize more than 95% of endometrial carcinomas. The presence of peritoneal-free cancer cells was identified morphologically in 27 of 182 lavages (14.8%) and ICC in 50 of 182 (27.5%), with a significant improvement (p <0.0001). Five-year survival analysis, comparing results of ICC and cytodiagnosis, demonstrated a significant decrease of disease-free survival in patients with peritoneal microscopic disease. Furthermore, multivariate analysis showed that ICC diagnosis of PWs is an independent prognostic factor. Data indicate that the use of selected MAbs allows one to identify cytologically false-negative cases, providing results that are highly predictive of a worse clinical outcome.