A single germ line mutation in BRCA1, (185delAG) is detected in a substantial portion of Jewish Israeli patients with ovarian cancer. Whether disease phenotypes differ in BRCA1 mutation carriers and sporadic cases is presently a subject for debate. To gain insight into this issue, we analysed tumours from 65 Jewish women with ovarian cancer, 29 (45%) were 185delAG BRCA1 mutation carriers, and 36 (55%) were non-carriers of any of the predominant Jewish mutations in BRCA1 or BRCA2 (sporadic). In 19/29 mutation carriers (66%) diagnosis was made prior to age 60 years, compared with 14/36 (39%) of the non-carriers (P=0.03; Yates corrected P=0.06). Low malignant potential ('borderline') tumours were detected less frequently among carriers (2/29; 7%) than non-carriers (9/36; 25%) (P=0.03; one tail P=0.05). Immunohistochemical analysis in invasive carcinoma (n=54) showed that 17/27 carriers (63%) and 18/27 non-carriers (67%) had positive nuclear staining with a p53 antibody. In 4/27 carriers (15%) and 3/25 non-carriers (12%), 25% or more of the tumour cells stained positive for Ki-67, an insignificant difference. Results were not altered by including borderline tumours (n=11) in these analyses. We conclude that the rate of TP53 inactivation and proliferative index in ovarian cancer, are similar for 185delAG BRCA1 mutation carriers and sporadic cases.