Risk-adjusted survival among HLA-A, -B serologic, and -DRB1 allele-matched pairs by number of mismatched class I loci. Survival after transplantation was analyzed as a function of the number of class I mismatches detected by high-resolution HLA typing in HLA-A, -B low-resolution, and -DRB1 high-resolution matched donor-recipient pairs. The data presented are adjusted for competing risk factors using the proportional hazards model, rather than univariate analysis. One or more additional mismatches led to poorer risk-adjusted survival (P = .0003).