We extract and present high-resolution HLA allele and haplotype frequency data available from the National Marrow Donor Program databases from four major U.S. census categories of race and ethnicity. Population-based high-resolution HLA frequencies defined on the basis of from one to five loci are presented and made available online (http://bioinformatics.nmdp.org/haplotype2006). In addition, a discriminatory classification of HLA allelic variation on the basis of observed population allele frequencies (common, rare and unseen) for HLA A, C, B, DRB1, DQA1, and DQB1 is introduced. The electronic availability of this information will be useful for projects central to the typing and use of population data in HLA applications.