Pregnancy coexisting with evolutive malignant blood disease (Hodgkin's disease, acute leukemia, non-Hodgkin's lymphoma, chronic myeloproliferative disorder) is a therapeutic dilemma because of possible adverse reactions associated with the use of cytostatic agents. Therapeutic abortion, when needed, must be proposed only after a careful evaluation of the following parameters: the emergency of treatment, the prognosis of the disease, the term of pregnancy, the risks of therapy for the foetus and the mother, and the psychosocial context. From the clinical data published so far, the teratogenicity of cytostatic drugs seems to be minimal after the second trimester, and the outcome of pregnancy is often favorable, whatever the hemopathy. Radiation therapy must be used very cautiously and only in supradiaphragmatic areas. An overview of specific problems is done for each category of malignant blood disease.