Polymorphic products of genes in the HLA region contributing to variability in the course of human immunodeficiency virus type 1 (HIV-1) infection were identified by screening 375 Caucasian seroconverters who were aggregated from 3 cohorts. AIDS-free time was related to numerous (15) class I alleles, alone or in conjunction with transporter protein variants, to homozygosity at the A or B locus, and to alleles of two class II haplotypes. A prognostic scoring algorithm derived from the 3 cohorts captured multiple HLA contributions to protection or to risk (relative hazard = 0.57–60 per unit increase in score, all P ≪.001). The impact of HLA was strong and appeared independent of the effects of chemokine receptor/ligand polymorphisms and antiretroviral treatment. The algorithm also predicted divergent rates of CD4⁺ cell decline in 2 other groups, totaling 227 seropositive persons (P = .06 — <.001). Confirmation of these relationships should encourage investigation of HIV-1 antigen processing and presentation mediated by polymorphisms in the HLA region.