Background: It is evident that smoking is causing disease and increased mortality in general. Recently published data are now suggesting that smoking might increase both the overall mortality in women diagnosed with breast cancer but also increase their risk of dying from their breast cancer. Methods: A systematic review and meta-analysis on smoking status in women diagnosed with breast cancer, their mortality rate and cause of death. Based on all cohort studies published within the last ten years. Results: Twelve studies met our inclusion criteria, and 400,944 women diagnosed with primary invasive breast cancer was included. Hazard ratio (HR) for breast cancer associated death in former smokers was 1.02 (0.93, 1.12) and for current smokers 1.28 (1.17, 1.41) when compared to never smokers. For all-cause death, the HR for former smokers was 1.12 (1.04, 1.19), and for current smokers 1.52 (1.32, 1.76) when compared to never smokers. Conclusions: This large systematic review and meta-analysis found a 28% increase in breast cancerassociated mortality in those who were current smokers compared to never smokers. The mortality in former smokers was equal to the one found in never smokers. This indicates that breast cancer patients ceasing to smoke can lower their risk of dying from their breast cancer disease dramatically, and possibly regain the risk of a never smoker.