['Endothelial dysfunction plays a central role in atherosclerotic progression and cardiovascular complications of type 2 diabetes mellitus (T2DM). Given the role of nitric oxide in the vascular system, we aimed to test hypotheses of synergy between the common endothelial nitric oxide synthase (eNOS) Asp298 allele and T2DM in predisposing to acute myocardial infarction (AMI).', 'In a population-based patient survey with 403 persons with T2DM and 799 healthy subjects from the population without diabetes or hypertension, we analysed the relation between T2DM, sex and the eNOS Asp298 allele versus the risk for AMI.', 'In an overall analysis, T2DM was a significant independent risk factor for AMI. In patients with T2DM, homozygosity for the eNOS Asp298 allele was a significant risk factor (HR 3.12 [1.49-6.56], p = 0.003), but not in subjects without diabetes or hypertension. Compared to wild-type non-diabetic subjects, all patients with T2DM had a significantly increased risk of AMI regardless of genotype. This risk was however markedly higher in patients with T2DM homozygous for the Asp298 allele (HR 7.20 [3.01-17.20], p < 0.001), independent of sex, BMI, systolic blood pressure, serum triglycerides, HDL -cholesterol, current smoking, and leisure time physical activity. The pattern seemed stronger in women than in men.'] Is the Asp298 allele of endothelial nitric oxide synthase a risk factor for myocardial infarction among patients with type 2 diabetes mellitus?