Unrelated donor transplant therapy for chronic myelogenous leukemia is both feasible and effective. As discussed in this article, clinical outcome can be predicted based on several patient characteristics and transplant conditions. Highly selected subsets of patients experience outcomes not appreciably different from recipients of related donor transplants. In many cases, however, unrelated donor transplant is associated with significant peritransplant mortality and other complications. The impact of recent improvements in donor-recipient typing, marrow procurement, graft-versus- host disease prevention and treatment, medical support, and donor selection should soon become apparent.