Objective. To estimate the likelihood of occult cancer diagnosis at prophylactic oophorectomy in BRCA1 and BRCA2 carriers in different age groups and to determine the histopathology of these lesions. Methods. We describe a series of 159 female BRCA1 or BRCA2 carriers who underwent prophylactic oophorectomy at the University Health Network, Toronto from January 1, 1992 to June 30, 2004. Results. Seven (4.4% ) occult cancers were detected at pathologic examination. None of the 159 subjects had clinical signs or symptoms of ovarian carcinoma prior to, or at the time of, surgery. Only two cancers were grossly visible at surgery. There were 94 BRCA1 carriers, of whom six were found to have an occult cancer (6.4% ). In contrast, only one of the 65 BRCA2 carriers was found to have an occult cancer (1.5% ). Three of the seven cases of occult malignancy involved the fallopian tube and not the ovaries. Conclusion. Approximately 6% of BRCA1 carriers and 2% of BRCA2 carriers who undergo prophylactic salpingo- oophorectomy will be found to have occult carcinomas if the ovaries and tubes are rigorously examined. A significant proportion of these appear to originate in the fallopian tube. No cancers were detected among women who had the operation at age 39 or younger. Objective. To estimate the likelihood of occult cancer diagnosis at prophylactic oophorectomy in BRCA1 and BRCA2 carriers in different age groups and to determine the histopathology of these lesions. Methods. We describe a series of 159 female BRCA1 or BRCA2 carriers who underwent prophylactic oophorectomy at the None of the 159 subjects had clinical signs or symptoms of ovarian carcinoma prior to, or at the University Health Network, Toronto from January 1, 1992 to June 30, 2004. Results Seven (4.4%) occult cancers were detected at pathologic examination. Only two cancers were grossly visible at surgery. There were 94 BRCA1 carriers, of whom six were found to have an occult cancer (6.4%). In contrast, only one of the 65 BRCA2 carriers was found to have an occult cancer (1.5%). Three of the seven cases of occult malignancy involved the fallopian tube and not the ovaries. Conclusion. Approximately 6% of BRCA1 carriers and 2% of BRCA2 carriers whoready prophylact A significant proportion of these appear to originate in the fallopian tube. No cancers were detected among women who had the operation at age 39 or younger.