Pelvic or peritoneal washing cytology (PWC) is a most useful indicator of subclinical peritoneal spread of ovarian cancer and thus provides valuable staging and prognostic information, particularly for nonserous ovarian carcinomas. However, PWC's role in endometrial cancer staging is less clear. Detection of malignant cells in peritoneal washings relies upon identification of nonmesothelial cells and their arrangement. While high-grade carcinoma can be easily identified, a number of benign conditions like reactive mesothelial cells, endosalpingiosis, and endometriosis may mimic serous borderline tumors and low-grade serous carcinomas. The presence in these benign conditions of ciliated cells and absence of single atypical cells, marked nuclear atypia, mitotic activity, or two distinct cell populations should help to avoid errors. In addition, close correlation with clinical history and the results of current or prior surgical specimens should help clinch the diagnosis. Additional techniques like cell blocks and ancillary studies can facilitate an accurate diagnosis.