HLA-DQ alleles are strongly associated with IDDM susceptibility and protection. Studies assessing the molecular properties of HLA-DR, a HLA class II locus in linkage disequilibrium with HLA-DQ, have made substantial contributions toward elucidating the structure and function of HLA class II molecules. Reports on the molecular properties of HLA-DQ are now following and have revealed interesting observations regarding the stability of HLA-DQ alphabeta heterodimers. Future work is expected to provide an understanding of the mechanism by which HLA-DQ is associated with IDDM susceptibility and protection.