A growing number of young breast cancer survivors consider reproductive health issues, including subsequent fertility and pregnancy, of great importance, but many questions regarding safety remain unanswered. We conducted a comprehensive literature search and review of published articles, control-matched, population-based, and co-operative group reports that addressed various aspects of pregnancy after breast cancer (patients' expectations, fertility damage, assessment and preservation, maternal and fetal outcome, breast feeding). Overall, available data support pregnancy and breast feeding after breast cancer as safe and feasible for women at low risk of recurrence. This retrospective and population-based evidence is, however, frequently incomplete; usually not representative of the entire population, it can be biased by patients' related effects or underpowered and is often not controlled for biological factors and risk determinants in the statistical model used. Before making any definitive assumption on this delicate and fundamental aspect of a woman's life after breast cancer, we should demonstrate without any reasonable doubt that the scattered information available today is scientifically sound. The Breast International Group and North American Breast Cancer Group are planning a global prospective study in young women with endocrine responsive, early breast cancer who desire pregnancy, to assess both patients' and pregnancy outcomes. The trial will include an observational phase investigating the feasibility and impact of a temporary treatment interruption to allow conception and an experimental phase investigating the optimal duration of the subsequent endocrine treatment after delivery or the last failed attempt to get pregnant.