The results of our study show that the presence of the TCF7L2 rs7903146 T allele in individuals with T2DM was associated with increased secretion of insulin, proinsulin, and C-peptide in response to a meal when compared with noncarriers of this allele, and no differences in serum glucagon or glucose concentrations. Here, TCF7L2 is linked to type 2 diabetes mellitus.