Reduced-intensity conditioning (RIC) preparative regimens are now widely used in umbilical cord blood (UCB) transplantation. Developed to reduce the rate of transplant-related morbidity and mortality as in adult stem cell donor transplantation, they are becoming more widely accepted. Results from RIC UCB series show a shortened time to engraftment, ranging from 12 to 24 days, with rates of TRM that generally do not exceed the rates seen with myeloablative UCB transplantation. There does not seem to be a convincing trend toward an increase in the rate of malignant relapse after RIC UCB transplantation, despite the lower intensity of the conditioning regimen. In this review, the results from several RIC UCB series are reviewed, comparisons with myeloablative UCB experiences are made and hypotheses regarding the engraftment potential of UCB after RIC regimens are discussed. In addition, a strategy for the optimal use of RIC regimens and UCB transplantation is presented.