Approximately 1 in 1,000-2,000 pregnancies are complicated by cancer. Today, different treatment options are considered as safe during pregnancy: chemotherapy, radiotherapy, surgery, or a combination of these. Surgery is considered safe during all trimesters of pregnancy; radiotherapy can be administered during the first and the second trimester, and chemotherapy after the first trimester of pregnancy. The placenta, acting as a barrier between the mother and the fetus, plays a key role in the safe administration of chemotherapy during pregnancy. A few studies have investigated the short- as well as the long-term health, general development, and cognitive and cardiac outcomes on children exposed to chemotherapy in utero. In general, these results were reassuring. Nevertheless, better safety data are required. This means data with longer follow-up periods and comparison with appropriate control groups. Moreover, important biasing factors should be taken into account when interpreting these results. Firstly, a great proportion of children were born prematurely due to the maternal condition. Preterm birth in general has been associated with cognitive impairment. Secondly, cancer during pregnancy is clearly a stressful situation, and maternal stress is associated with attention deficits. In sum, we state that chemotherapy can be administered safely after the first trimester of pregnancy. Moreover, iatrogenic prematurity in order to start postpartum administration of chemotherapy should be avoided. Nonetheless, decisions concerning treatment in these specific cases should always be made in a multidisciplinary setting with internationally recognized expertise in the coexistence of cancer and pregnancy.