We summarize the cases of four women with acute myeloid leukemia (AML) and of one with acute lymphoid leukemia (ALL) presenting in the first, second and third trimester of pregnancy. Remission of AML was induced by doxorubicin, vincristine, and cytosine arabinoside. The ALL case was treated with vincristine and prednisone initially, and subsequently with vindesine for maintenance. Four patients entered a complete (3 AML and the ALL case), and one (AML) a partial remission. This patient was delivered of a normal, 3140 g, male infant by Caesarian section in the 38th gestational week and 1 month later she died of her disease. One patient (AML, promyelocytic type) who presented in the 10th week of pregnancy underwent elective abortion while in remission after induction treatment. The patient with ALL gave birth to a normal, full-term, male infant by Caesarian section. The two other patients (AML) had spontaneous deliveries of normal male infants in the 37th and 38th weeks of pregnancy. Growth and development of three of the children are normal at 12, 36, and 37 months of life while the fourth child was lost to follow-up evaluation. The disease relapsed in all mothers but they are still alive at 15 (ALL), 37, and 42 months after diagnosis. We feel that current chemotherapy could improve the high post-partum maternal mortality rate and the chance of producing live babies without excessive risk to the fetus or the mother, even if administered relatively early in the course of pregnancy.