Pregnancy is infrequently complicated by the diagnosis of a concurrent breast cancer. This presents a particularly complicated clinical problem. The treatment of breast cancer in young women involves a number of difficult decisions regarding therapy. These decisions become even more complex when the concerns of the safety of an unborn child are added to the equation. For breast cancers diagnosed late in the third trimester, it is relatively straight forward to delay therapy until after delivery. For women diagnosed earlier in pregnancy, there are legitimate concerns that delays in therapy may adversely affect outcomes. While there are no randomized trials addressing the optimal treatment of women in this situation, there are case reports, case series, and cohort experiences that provide some insight. There are recommendations available from an international working group and from the National Comprehensive Cancer Network that address the treatment of women in this situation. There is general consensus that both surgery and chemotherapy are relatively safe after the first trimester of pregnancy. It is generally agreed that therapeutic radiation, if necessary, should be delayed until completion of pregnancy.