Prophylactic surgery including hysterectomy and bilateral salpingo-oophorectomy (BSO) is recommended in breast cancer susceptibility gene (BRCA)-positive women, whereas in women from the general population, hysterectomy plus BSO may increase the risk of overall mortality. The effect of hysterectomy plus BSO on women previously diagnosed with breast cancer is unknown. We used data from a population-base data linkage study of all women diagnosed with primary breast cancer in Queensland, Australia between 1997 and 2008 (n = 21,067). We fitted flexible parametric breast cancer-specific and overall survival models with 95% confidence intervals (also known as Royston-Parmar models) to assess the impact of risk-reducing surgery (removal of uterus, one or both ovaries). We also stratified analyses by age 20-49 and 50-79 years, respectively. Overall, 1,426 women (7%) underwent risk-reducing surgery (13% of premenopausal women and 3% of postmenopausal women). No women who had risk-reducing surgery compared to 171 who did not have risk-reducing surgery developed a gynaecological cancer. Overall, 3,165 (15%) women died, including 2,195 (10%) from breast cancer. Hysterectomy plus BSO was associated with significantly reduced risk of death overall [adjusted hazard ration (HR), 0.69; 95% confidence interval (CI), 0.53-0.89; p = 0.005]. Risk reduction was greater among premenopausal women, whose risk of death halved (HR, 0.45; 95% CI, 0.25-0.79; p < 0.006). This was largely driven by reduction in breast cancer-specific mortality (HR, 0.43; 95% CI, 0.24-0.79; p < 0.006). This population-based study found that risk-reducing surgery halved the mortality risk for premenopausal breast cancer patients. Replication of our results in independent cohorts and subsequently randomised trials are needed to confirm these findings. What's new? Risk-reducing surgery involving a combination of hysterectomy and bilateral salpingo-oophorectomy (BSO) is recommended for women who are BRCA-positive. However, it remains unclear whether the combined approach is beneficial for women actually diagnosed with breast cancer. Here, analysis of data on 21,067 women diagnosed with primary breast cancer in Queensland, Australia, between 1997 and 2008 shows that risk-reducing surgery cut mortality in half for premenopausal patients. Prophylactic surgery, however, did not appear to benefit postmenopausal patients. The findings challenge the idea that non-invasive endocrine treatment is as effective as prophylactic surgery for premenopausal women with breast cancer.