Type 1 diabetes is an autoimmune disease caused by a combination of genetic and environmental factors. On the basis of a genomic search for linkage in a Bedouin Arab family with 19 members with type 1 diabetes, we previously mapped the IDDM 17 locus to the chromosome 10q25.1 region. The result from a recent genome scan showed suggestive evidence of linkage of IDDM 17 in a subset of Caucasian families in which all affected individuals have DR3, indicating that the IDDM 17 locus might have a measurable effect in Caucasian populations from the United Kingdom and the United States. High-resolution SNP typing provides strong evidence of linkage disequilibrium to the IDDM 17 locus.