To estimate the 15-year survival following a diagnosis of stage I breast cancer among women who carry a BRCA1 mutation and to determine predictors of mortality, including the use of chemotherapy. Patients were 379 women with stage I breast cancer for whom a BRCA1 mutation had been identified, in herself or in a close family member. Patients were followed for up to 15 years from the initial diagnosis of breast cancer. Survival rates were estimated for women by age, tumor size (≤ 1 cm; > 1 cm), ER status (±), and by chemotherapy (yes/no). 42 women died of breast cancer in the follow-up period (11.2 %). Survival rates were similar for women with cancers of size 0-1.0 cm and size 1.1-2.0 cm. Of the 267 women in the study who used chemotherapy, 21 had died (7.9 %) compared to 21 deaths among 112 women who did not receive chemotherapy (18.8 %; p = 0.002). The 15-year survival was 89.4 % for women who received chemotherapy and was 73.1 % for women who did not receive chemotherapy (p = 0.08; log rank). The adjusted hazard ratio for death following a diagnosis of stage I breast cancer associated with chemotherapy was 0.53 (95 % CI 0.28-1.07; p value 0.06) after adjusting for age of diagnosis, tumor size, and estrogen receptor status. This was statistically significant only among women with ER-negative breast cancers (HR = 0.28; 95 % CI 0.10-0.79; p = 0.02). BRCA1 positive women who are treated for stage I breast cancer with chemotherapy have better survival than those who do not receive chemotherapy. The difference cannot be explained by other prognostic factors. All women with invasive breast cancer and a BRCA1 mutation should be considered to be candidates for chemotherapy.