In this study, we estimate the amount of human leukocyte antigen (HLA) genetic diversity in the global human population at three levels of population hierarchy: within populations; among populations within continents and among continents on large sets of HLA population data gathered during the last international histocompatibility and immunogenetics workshops and conferences. The results indicate that loci HLA-A, B, C, DRB1, DQA1 and DQB1 exhibit a higher amount of diversity among individuals of the same population than observed for neutral polymorphisms (average diversity of 90.3% compared with 84.4%-87.6% for neutral DNA markers). On the other hand, the value (84%) obtained for HLA-DPB1 is very similar to those observed for non-HLA nuclear markers, in agreement with other results suggesting the neutrality of this locus. In addition to the results of the hierarchical analysis of variance, selective neutrality tests indicate that loci B, C and DRB1 are the most affected by balancing selection. However, one cannot discriminate between a direct selective effect acting on those loci or a general effect of associative overdominance acting over the large HLA region (in linkage disequilibrium) encompassing those loci.