The National Marrow Donor Program has established a large and ethnically diverse registry of volunteer, unrelated stem cell donors. More than 9,000 patients world-wide have received transplants from NMDP donors. In recent years, substantial resources have been invested to increase that portion of the NMDP donor file with complete HLA-A, -B and -DR typing. While this effort has improved the likelihood of patients identifying a suitable matched unrelated donor, it has also focussed more attention on issues surrounding donor availability. Several initiatives underway or planned are intended to improve donor availability and increase the overall success of the unrelated donor stem cell transplantation.