The interactions between pregnancy and breast cancer (BC) are complex. Overall, parity is associated with long-term protective effects against BC, however in a small group of susceptible patients, pregnancy can lead to the development of a form of BC with a particularly poor prognosis. Pregnancy-associated breast cancer (PABC) remains an under-studied but important and growing clinical problem worldwide. Several aspects of PABC, including risk factors and mechanisms involved in its occurrence and aggressiveness, are incompletely understood. This review aims to summarize the epidemiology, biology, patho-physiology and clinical characteristics of PABC. We emphasize that age at first pregnancy, absence of breastfeeding and family history stand out as possible risk factors for developing PABC that ought to be incorporated into clinical tools for assessing a woman's risk of developing PABC. Also, improved methods for identifying women at risk of developing PABC in the general population are needed.