Coronary artery disease (CAD) is a polygenic disease whose phenotypic manifestation depends on the interaction of a number of environmental factors. A number of genes, including the angiotensin-I-converting enzyme (ACE) gene, have been implicated in the pathogenesis of CAD. ACE could affect smooth muscle cell and fibroblast migration and proliferation, low-density lipoprotein (LDL) oxidation and endothelial cell function; these are all important factors in atherosclerosis. A polymorphic variant of the ACE gene correlates with higher circulating ACE levels and carries an increased risk of myocardial infarction, and cardiomyopathies. In this study, we sought to determine the distribution of ACE genotypes and the frequency of allele D in patients undergoing coronary angiography at our institution. DNA from 196 patients with angiographically proven CAD and 96 controls without CAD was amplified by polymerase chain reaction (PCR). The primers flanked the region of the ACE gene (intron 16) where the insertion (I) or deletion (D) of a 287-bp fragment results in the I/D polymorphism. PCR amplification of alleles I and D resulted in 490- and 190-bp products, respectively. In the control group, the relative allele frequencies of the polymorphism were similar to those of previously published European studies. The ACE genotype DD was present in 37.3% of patients with CAD as compared to 23.4% in the controls (p < 0.001, odds ratio 1.95, 95% confidence intervals (CI) 1.06-3.57). There was no association with the history of prior myocardial infarction. The genotype distribution in patients with single-vessel involvement was not significantly different from controls (p = 0.14). However, the DD genotype was significantly more common in patients having multivessel CAD when compared to single-vessel disease, indicating an association of this polymorphism with the extent of CAD. ACE genotype DD is more common in patients with multivessel CAD as compared to controls and to patients with single-vessel involvement, indicating that genotype DD is a genetic risk factor for extensive, multivessel CAD.