A prospective survey involving 544 searches of the US National Marrow Donor Program (NMDP) Registry was conducted to identify reasons why many patients who have apparent HLA-matched donors do not proceed to transplant. Coordinators at NMDP transplant centers, patients and referring physicians were surveyed shortly after the initial search, and follow-up surveys were sent to the coordinators as the search was ongoing. The death of the patient, worsening of the patient's medical condition and length of the search process were the most commonly cited barriers to transplantation. Other times a decision was made not to transplant through the NMDP due to the use of a donor from another source, a preference for chemotherapy or immunotherapy, hesitancy on the part of the transplant physician or patient, or because the patient did not require a transplant. Responses differed between U.S. and international cases. An unrelated donor outside the NMDP was the most common reason cited by international coordinators (46%), whereas the death of the patient was the most common reason among US coordinators (13%). The death of the patient was the second most common reason cited by international coordinators at 9%. Financial problems were listed by 41% of US coordinators as a potential barrier at the time of initial search, but only 5% indicated this as an actual barrier on a follow-up survey. Finances were cited as the most important reason 3% of the time overall, and 6% for African Americans and Asian/Pacific Islanders.