The sulfonylurea receptor (SUR) is a key component in glucose-stimulated insulin secretion. Obesity and NIDDM are frequently associated and share some metabolic abnormalities, suggesting that they might also share some susceptibility genes. Thus, the SUR encoding gene is a plausible candidate for a primary pancreatic β-cell defect and thus for hyperglycemia and weight gain. Through association and linkage studies, we have investigated the potential role of the SUR gene in families with NIDDM and in two independent sets of morbidly obese families. The exon 22 T-allele at codon 761 was more common in patients with NIDDM (7.7%) and morbid obesity (7.8%) than in control subjects (1.8%, P = 0.030 and P = 0.023, respectively). This variant was associated with morbid obesity (odds ratio 3.71, P = 0.017) and NIDDM (odds ratio 2.20, P = 0.04; association dependent on BMI). Although the frequencies for intron 24 variant were similar in all groups, morbidly obese patients homozygous for the c-allele had a more deleterious form of obesity. Sib-pair linkage studies with NIDDM in French Caucasian families gave no evidence for linkage to the SUR locus. However, in one set of the obese families, we found an indication for linkage with a SUR-linked microsatellite marker (D11S419, P = 0.0032). We conclude that in Caucasians, the SUR locus may contribute to the genetic susceptibility to NIDDM and obesity.