Breast cancers diagnosed during pregnancy and lactation typically have an aggressive phenotype and an advanced stage at presentation. The timing of treatment modalities in pregnant women is complex and requires multidisciplinary input. Alternatives which are relatively safe for both mother and fetus are available, though unforeseen risks may exist. Chemotherapy is not thought to be safe for a fetus during the first trimester; however, in women with high risk cancers, treatment should not be delayed. Thereafter, anthracycline based chemotherapy has a low incidence of fetal complications. Little evidence beyond case reports exists for taxanes or tamoxifen in pregnancy, and less is available regarding the safety of novel molecularly targeted therapeutics such as trastuzumab. The prognosis of breast cancer diagnosed during pregnancy and lactation is poor, largely because of advanced stage and aggressive phenotype; it is unclear whether pregnancy is an independent prognostic marker for poor outcome.