Bone marrow transplantation is an effective form of therapy for lethal immunodeficiency diseases and leukemia. Patients who are treated by bone marrow transplantation for these diseases have an improved outcome if treated early after diagnosis, before they have developed secondary complications. Recent advances in transplantation have allowed choices between several donor types. These alternative donor types are the subject of this analysis from the University of Minnesota. In these diseases, matched sibling donor bone marrow transplantation is the standard for comparison. In individuals with lethal immunodeficiencies (severe combined immune deficiency [SCID], Wiskott-Aldrich syndrome [WAS], Chédiak-Higashi syndrome [CHS]) who lack a sibling donor, unrelated transplantation has produced results that are almost equal to those of matched sibling transplants. Patients with high-risk acute lymphoblastic leukemia (ALL) who have received sibling or unrelated transplants have results that are superior to autologous donor transplants. In ALL, there is a need to use new therapies, eg, immunotoxins, to decrease the currently high relapse rate. In patients with acute myelogenous leukemia (AML) in first complete remission, results are excellent and comparable using related and autologous donors. Results in non-first-remission AML are inferior and do not differ if related, unrelated, or autologous transplants are used. In chronic myelogenous leukemia (CML), early survival results are superior using autologous and related transplants as compared with unrelated transplants.