The prevalence of AIDS now approaches 1% in patients with hemophilia and laboratory evidence of abnormal immunoregulation is found in 50% of patients with severe hemophilia. Current evidence indicates that a human retrovirus HIV/LAV is the etiologic agent which can be transmitted through the administration of blood products. We reported 7 cases in childhood, 5 acute leukemia, 1 metastatic neuroblastoma, and 1 severe aplastic anemia in whom AIDS occurred after administration of blood products. To date 5 patients are alive and 2 have died of infections. It is suggested that the use of steroids or antineoplastic agents increases the incidence of AIDS in patients infected with HIV/LAV because of altered immune suppression. The maintenance treatment is difficult in these patients. The widespread use of HIV serology to screen donated blood should help to prevent AIDS transmission in leukemic patients.