Genetic abnormalities of the renin-angiotensin system have been suggested as risk factors for the development of diabetic retinopathy and nephropathy. And also it has recently been shown to be associated with coronary artery disease in general population and diabetic patients. However, the relationship between the genetic polymorphism of the renin-angiotensin system and diabetic microvascular complication and coronary artery disease remains still controversial. We analyzed the ACE genotype in 389 patients with non-insulin dependent diabetes mellitus (NIDDM) aged over 30. A total of 169 subjects (48 diabetic and 121 non-diabetic) underwent coronary angiography was included in this study to evaluate the effect of ACE genotype on coronary artery disease. The insertion/deletion (I/D) polymorphism was determined by the polymerase chain reaction (PCR). ACE genotypes was consisted of 18.8% DD homozygotes, 50.9% ID heterozygotes, and 30.3% II homozygotes in all subjects. Age, duration of diabetes, BMI, systolic and diastolic blood pressure were not different significantly among three genotypes. There was no significant difference in the genotype distribution between patients with diabetic nephropathy (21.7% DD, 48.1% ID, 30.2% II) and those without nephropathy (14.4% DD, 52.3% ID, 33.3% II). And also there were no significant relationships between genotype distribution and retinopathy (patients with retinopathy; 17.6% DD, 45.9% ID, 36.5% II vs. without retinopathy; 12.1% DD, 47.5% ID, 40.4% II) and coronary artery disease in diabetic patients (with coronary artery disease; 63.2% ID+DD, 36.8% II vs. without coronary artery disease; 70.0% ID+DD, 30.0% II). These results suggest that ACE genotype is unlikely to serve as clinically useful predictors of diabetic microvascular complications and coronary artery disease in patients with NIDDM in Korea.