The purpose of this study was to determine the rate and outcomes of pregnancies subsequent to breast cancer in Korea, and the effect of such pregnancies on the prognosis of women who survived breast cancer and subsequently conceived.We followed a total of 31,761 Korean women 45 years of age or younger who were treated for primary breast cancer from 2002 to 2010. We also included follow-up surveys that were conducted through December 2011. We identified recurrence and mortality from breast cancer using data linked to the Korea National Health Insurance database. We used propensity score matching of the study cohort to analyze the risks of recurrence and mortality from breast cancer depending on pregnancy.Within our sample, 992 women (3.1%) became pregnant after receiving treatment for breast cancer. Of those, 622 (67.5%) successfully delivered; the remaining 370 (32.5%) failed to deliver. After propensity score matching, we found that the women who became pregnant after breast cancer did not have a different risk of recurrence (hazard ratio [HR], 0.503; 95% confidence interval [CI], 0.434 to 0.584) and death (HR, 0.520; 95% CI, 0.397 to 0.681), compared with those who did not conceive after breast cancer treatment.Our study is the first to report outcomes for Korean women who survived breast cancer and subsequently conceived. Women who survived breast cancer and subsequently became pregnant did not show a poorer survival outcome, compared with those who did not become pregnant.