BACKGROUND: Umbilical cord blood (UCB) is now a commonly used resource for hematopoietic stem cell (HSC) transplantation; great effort has been put forth in standardizing protocols for processing, storage, and testing of UCB units. Because UCB units are selected on an individual basis to maximize the chance of engraftment, loss of container integrity may have adverse effects on patient outcome. STUDY DESIGN AND METHODS: All bag breaks involving UCB units thawed for transplantation at our institution between January 1, 2000, and May 31, 2006, were identified. Information on various laboratory variables and the clinical consequences of UCB bag breaks was obtained from the deviation database of the Clinical Cell Therapy Laboratory (CCTL). Patient medical charts were reviewed for infusion-related data. RESULTS: The incidence of bag breaks over a 61/2-year period was 3.5 percent. A majority of cases of loss of container integrity occurred in units that had been cryopreserved for more than 2 years (75%) and resulted in minimal loss of product. There were no significant decreases in quantity or quality of UCB, as determined by various quality control tests; no adverse clinical outcomes related to receiving a broken UCB unit were noted except increased antibiotic usage. CONCLUSION: There was a relatively low incidence of UCB bag breaks in this study that did not result in significant loss of UCB or adverse clinical outcomes. With the FDA considering licensure of UCB for hematopoietic reconstitution, improvement in container design and possibly guidelines limiting length of storage will likely be addressed in detail.