Genome-wide mapping studies have provided evidence of a type 1 diabetes susceptibility gene (IDDM8) that is located on chromosome 6q27. However, association studies of IDDM8 have so far been negative. The purpose of this investigation was to determine a linkage disequilibrium (LD) map in the chromosome 6q27 region and to better localize IDDM8. A physical map of nearly 1 Mb containing the chromosome 6 telomere was constructed, and polymorphic markers spanning this region were defined. Haplotypes composed of the markers in LD were tested for association with type 1 diabetes in 266 families. A microsatellite marker allele and multiple haplotypes were associated with IDDM8, which suggests localization of this type 1 diabetes susceptibility gene to the terminal 200 kb of chromosome 6.