HLA population data can be applied to estimates of waiting time and probabilities of donor compatibility. Registry data were used for derivation of HLA antigen and haplotype frequencies in a 1996 report. At that time there were several instances of significant deviation from Hardy Weinberg Equilibrium (HWE). Because molecular typing has been increasingly used since 1996, analysis of recent donor phenotypes should provide more accurate HLA frequencies.HLA frequencies were derived from the phenotypes of 12,061 donors entered into the Organ Procurement and Transplantation Network registry from January 1, 2003 to December 31, 2004. Frequencies for HLA-A;B;DR and HLA-A;B, DR, DQ haplotypes were derived from 11,509 and 10,590 donors, respectively. Frequencies of the allele groups encoding serologic antigens were obtained by gene counting and haplotype frequencies were estimated using the expectation maximization algorithm. Fit to HWE was evaluated by an exact test using Markov Chain Monte Carlo methods.There was clear evidence of improved definition of rarer HLA antigens and haplotypes, particularly among minorities. The reported frequencies of broad antigens decreased overall for HLA-A, B, and DR, with concomitant increases in split antigens. Allele group genotypes among the major ethnic groups were in HWE with the single exception of HLA-A locus alleles among Asians. Improved HLA definition also permitted the first report of DR;DQ and A;B;DR;DQ haplotypes among U.S. donors.The noted improvements in HLA definition and the overall lack of significant deviation from HWE indicate the accuracy of these HLA frequencies. These frequencies can therefore be applied for representative estimates of the U.S. donor population.