Résumé : At least one in a thousand pregnancies is complicated by cancer and, as the maternal age at pregnancy increases, numbers are growing. If chemotherapy cannot be postponed, both doctors and patients face complex medical and ethical issues. There is a conflict between optimal maternal therapy and fetal wellbeing. Treatment during the first trimester increases the risk of congenital malformations, spontaneous abortions and fetal death. Second and third trimester exposure is less risky, but it can cause intrauterine growth retardation and low birth weight. Other effects on pregnancy after the first trimester include premature birth, stillbirth, impaired functional development, myocardial toxicity and myelosuppression. Counseling and management of these cases are difficult, because literature is mostly represented by case reports or retrospective series while randomized prospective studies or guidelines are lacking. Moreover, personal experience is often scanty due to the rarity of the condition. This article reviews the available data regarding the different aspects of systemic treatment of cancer during pregnancy to help oncologist and obstetricians in counseling their patients and treat them accordingly.