The Met55Val polymorphism in the small ubiquitin-like modifier 4 (SUMO4) gene has been associated with susceptibility not only to type 1 diabetes, but also to type 2 diabetes and diabetic nephropathy. We tried to confirm the association with susceptibility to type 2 diabetes and to investigate its role in diabetic vascular complications. The polymorphism was genotyped in two independent Japanese samples (Wakayama and Tokyo) by the TaqMan method. Susceptibility to type 2 diabetes and prevalence of diabetic vascular complications (coronary heart disease, cerebral infarction, retinopathy, and nephropathy) were evaluated by case-control study and multivariate logistic regression analysis, respectively. There were no significant differences in the frequency of alleles or genotypes between patients and controls. The Val allele, however, was associated with higher prevalence of coronary heart disease in patients in both groups (Wakayama, n=423, odds ratio, 1.64; 95% confidence interval, 1.02-2.64; P=0.041; Tokyo, n=451, odds ratio, 1.58; 95% CI, 1.07-2.34; P=0.021, in an additive model, respectively). No significant associations were observed with other diabetic vascular complications. Although association of the polymorphism with susceptibility to type 2 diabetes or nephropathy was not replicated, an association of the polymorphism with risk of coronary heart disease in type 2 diabetes is suggested.