Background: The continued growth in the uses of umbilical cord blood (UCB) will require the development of meaningful postthaw quality assays. This study examines both conventional and new measures for assessing UCB quality after long-term storage. Study Design and Methods: The first arm of the study involved thawing UCB in storage for short (approx. 1 year) and long periods of time (>11 years). Conventional postthaw measures (colony-forming units [CFU], total nucleated cell counts, CD34+45+) were quantified in addition to apoptosis. The second arm of the study involved taking units stored in liquid nitrogen and imposing a storage lesion by storing the units in -80°C for various periods of time. After storage lesion, the units were thawed and assessed. Results: In the first arm of the study, there was little difference in the postthaw measures between UCB stored for short and long periods of time. There was a slight increase in the percentage of CD34+45+ cells with time in storage and a reduction in the number of cells expressing apoptosis markers. When moved from liquid nitrogen to -80°C storage, the nucleated cell count varied little but there was a distinct decrease in frequency of CFUs and increase in percentage of cells expressing both early and late markers of apoptosis. Conclusion: Nucleated cell counts do not reflect damage to hematopoietic progenitors during long-term storage. Expression of caspases and other markers of apoptosis provide an early biomarker of damage during storage, which is consistent with other measures such as CFU and percentage of CD34+45+ cells.