Acute leukemia was diagnosed in five pregnant patients who received chemotherapy during the course of pregnancy. Three were undergoing chemotherapy at conception. One patient died in the fifth month of pregnancy and the anatomic study of the fetus was normal. Four babies had low birth weights at birth. Of the four one was born prematurely, but without malformations. Later development was normal. The results are reviewed and compared with data from the literature, leading to the conclusion that pregnancy is not an absolute contraindication for cytostatic treatment, except in the first trimester, in which cytostatic treatment should be avoided.