This study presents the cytologic features of peritoneal washings, with particular emphasis on the cytologic discrimination among serous, mucinous, and endometrioid adenocarcinoma of the ovary. We selected histologically confirmed 27 cases of peritoneal washing : 8 cases of serous cystadenocarcinomas, 5 cases of mucinous cystadenocarcinomas, and 14 cases of endometrioid adenocarcinomas. The most frequent cytologic pattern of three tumors was clusters. Ball pattern was found in serous cystadenocarcinoma(36%) and acinar pattern in endometrioid adenocarcinoma(36%). Mucinous adenocarcinoma showed mucoid background(100%) and endometrioid adenocarcinoma revealed inflammatory background(43%). The cytoplasmic vacuoles were noted in 80%, 13%, and 43% of mucinous, serous, and endometriold adenocarcinoma, respectively. The endometrioid adenocarcinoma showed prominent nucleoli(64%). In conclusion, the cytologic findings of mucinous cystadenocarcinoma were different from that of serous and endometrioid carcinomas, such as mucoid background, abundant cyytoplasm with vacuolated cytoplasm, and peripherally located cytoplasm. Although endometriold carcinoma showed acinar pattern and prominent nucleoli, the differential diagnosis between serous cystadenocarcinoma and endometrioid adenocarcinoma in peritoneal washing cytology was was always possible.