To better understand the role of germline BRCA mutations in ovarian cancer in Ashkenazi Jews, we tested 29 consecutive patients admitted to our service for the three mutations common in this ethnic group. These mutations are 185delAG and 5382insC in BRCA1 and 6174delT in BRCA2. Six patients had both breast and ovarian cancer, and 23 had ovarian cancer only. In the first group, all women had germline mutations, 2 with each mutation. Of 23 ovarian cancer patients, 11 were carriers (48%): 6 of 185delAG, 2 of 5382insC, and 3 of 6174delT. Regarding family history, of 13 women with no family history, 3 (23%) were carriers. Of 10 women with any family history of breast or ovarian cancer, 8 (80%) were carriers. We discuss possible explanations for this surprisingly high carrier rate, including a high proportion of familial disease coupled with lack of adequate family history, lower penetrance than previously expected, or increasing penetrance in recent generations due to nongenetic factors. Our data suggest that genetic testing is merited in all Ashkenazi women with ovarian cancer, regardless of family history.