HLA matching between a donor and recipient is the single most important factor affecting clinical outcomes following hematopoietic cell transplantation (HCT). The likelihood of finding a match, or match rate, is calculated by combining HLA genetic haplotypes with their known frequencies in specific populations. This session will discuss what we have learned about historical match rates, how they might be affected by geographic location within the US and how we can use population genetics to predict future match rates for specific populations in a registry size analysis. In addition, this session will examine the impact of historical migrations on the genetic diversification within racial or ethnic groups.