OBJECTIVE Prophylactic oophorectomy (PO) is an accepted treatment strategy for women who are at high risk for the development of ovarian carcinoma, particularly women who are BRCA mutation-positive. This study sought to assess the utility of peritoneal lavage cytology at the time of PO in detecting occult malignancy in this group of patients. METHODS Thirty-five high-risk women, who were not suspected of having any malignancy or ovarian mass, underwent peritoneal lavage at the time of PO. Thirty-one of the thirty-five women had undergone BRCA mutation analysis (BRCA1+, 18; BRCA2+, 10; BRCA-, 3). Intensive histopathologic examination was used in all 35 cases to identify occult carcinoma. Lavage specimens were reviewed for the presence of malignant cells and endosalpingiosis. The cytologic review was conducted without knowledge of either the histopathologic or BRCA results. RESULTS In 32 of the 35 lavage specimens no malignancy was detected. In the remaining three cases malignant cells were detected; in two of these cases histopathologic examination confirmed an ovarian/tubal occult carcinoma. Two of these women were BRCA1 mutation positive. Endosalpingiosis was detected in the peritoneal lavage specimens of 7 of the 32 cases showing no evidence of malignancy. All of these 7 women were BRCA mutation positive or unknown. CONCLUSION Peritoneal lavage cytology can detect occult carcinoma at the time of PO and should be performed at PO. The significance of occult carcinoma detected by either histopathologic or cytopathologic examination is uncertain. Whether the prevalence of endosalpingiosis detectable by lavage cytology is increased in BRCA mutation-positive patients requires further study.