BACKGROUND: Because the frequency of umbilical cord blood (UCB) stem cell transplantation has increased, the quality of UCB available in banks is an important part of the success of UCB stem cell transplants. STUDY DESIGN AND METHODS: A quality assurance monitoring system was used to evaluate 268 UCB units provided to us for transplant by UCB banks in the United States and Europe. RESULTS: Quality issues were found in 151 (56%) of 268 units, and there were a total of 246 specific issues in 151 units. The issues involved quality control (54%), medical history (40%), and labels and documentation (6%). Risks to patients from these issues were likely in 10 percent, potential in 35 percent, and unlikely in 55 percent. CONCLUSION: Because standards have evolved over time, cord blood banks contain units that have different levels of quality. Some units have been placed in the usable inventory with incomplete test results and/or documentation or that may not meet the bank's own current criteria. Information about any quality or operating procedure deviation should be provided in sufficient detail and at the initiation of the search process so that transplant physicians can consider these quality issues against the unique value of a particular UCB unit.