The Type 1 Diabetes Genetics Consortium (T1DGC) sponsored an Autoantibody Workshop, providing data from a large number of type 1 diabetes-affected sibling pair families with multiple autoantibodies assayed (both islet and nonislet targets) and extensive genetic and clinical information. Multiple groups analyzed the autoantibody data and various forms of genetic data. The groups presented their results at the T1DGC Autoantibody Workshop and compared results across genes and autoantibodies. The reports of the analyses of the autoantibody data with genetic information are contained as individual articles in this supplement. There were several consistent findings that emerged from the T1DGC Autoantibody Workshop. The human MHC (HLA genes) is the major contributor to variation in the presence of islet and nonislet autoantibodies in subjects with established type 1 diabetes. The contribution of non-MHC genes/variants to autoantibody prevalence is dependent on the set of single nucleotide polymorphisms tested, the autoantibody evaluated, and the inclusion criteria for sample selection. On the basis of these results, the HLA alleles DRB1*0101 and DRB1*0404 and the PTPN22 R620W variant are consistently associated with autoimmunity in the T1DGC Autoantibody Workshop data.