This review dwells on the mostrelevant aspects of this problem: namely, the correlation between carriage ofcertain MHC II alleles and an increased (positively associated allele) orreduced (negatively associated allele) probability of developing the mostcommon autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis,multiple sclerosis, systemic lupus erythematosus, autoimmune thyroiditis, etc.The most universal haplotypes, DR3-DQ2 and DR4-DQ8, are positively associatedwith many of these diseases, while the universal alleleHLA-DRB1*0701 is protective. This evidence concerns the gene HLA-DRB1 and type 1 diabetes mellitus.