Common and rare variants of the hepatocyte nuclear factor 4alpha (HNF4A) gene have been associated with type 2 diabetes and related traits in several populations suggesting the involvement of this transcription factor in diabetes pathogenesis. Single nucleotide polymorphisms (SNPs) within a large haplotype block surrounding the alternate P2 promoter, located approximately 45 kb upstream from the coding region, have been investigated in several populations of varying ethnicity with inconsistent results. Additionally, SNPs located within the P1 promoter and coding region have also been inconsistently associated with type 2 diabetes. Characterization of variation across this gene region in Mexican-American populations has not been reported. We therefore examined polymorphisms across the HNF4A gene in a cohort of Mexican-American pedigrees and assessed their association with type 2 diabetes. We observed evidence for association of SNPs in the P2 promoter region with type 2 diabetes (P = 0.003) and its age at diagnosis (P = 0.003). The risk allele frequency (53%) was intermediate to that reported in Caucasian populations (20-27%) and Pima Indians (83%). No other SNPs were associated with either trait. These results support the possibility that a variant in the P2 promoter region of HNF4A, or variants in linkage disequilibrium within this region, contributes to susceptibility to type 2 diabetes in many ethnic populations including Mexican Americans.