We analyzed the clinical features of 25 ovarian cancer patients who were associated with germ-line mutations of BRCA1 from four site-specific ovarian cancer families and seven breast-ovarian cancer families in Japan. The average age at diagnosis was 51.1 years (range, 38-77 years). Histological examination revealed 24 serous cyst adenocarcinomas in 25 patients. In 23 patients with clear clinical records, 3 patients had stage I disease, 17 had stage III disease, and 3 had stage IV disease. Thirteen patients with stage III disease who were treated with cisplatin-containing chemotherapy following tumor reduction surgery showed more favorable outcomes in both the survival rate and disease-free intervals, compared with age- and treatment course-matched controls (5-year survival rate, 0.786 versus 0.303; median disease-free interval, 91.43 versus 40.92 months; P < 0.05 for both, by logarithmic rank test). Our statistical model for the inheritance of susceptibility to ovarian cancer was derived from the analysis of 26 patients and 19 healthy carriers of 12 families. The expected lifetime risk of ovarian cancer is about 80% for women with mutations of BRCA1. These results suggest that the clinical outcome of ovarian cancer with germ-line mutations of BRCA1 appears to be more favorable than that with sporadic cases and that the disease penetrance among pedigrees with germ-line mutations of the BRCA1 gene is substantially high.