Renin-angiotensin system is thought to play a role in coronary thrombosis and restenosis. Plasma angiotensin I-converting enzyme (ACE) activity is associated with an insertion/deletion polymorphism in the gene coding for ACE. The association among restenosis within coronary stents, the D/I polymorphism is analyzed in the present study. We are selected 50 patients who had undergone successful percutaneous transluminal coronary angioplasty, and angiography during 1 year after it for some reason. The I/D alleles were identified on the basis of polymerase chain reaction (PCR) amplification of the respective fragments from intron 16 of ACE gene. The differences between groups were tested by Chi-square test or Fisher exact test. Result from chi-square test and Fisher exact test shows the lack of differences between two groups with respect to sex, age, diabetes, hypertension, cholesterol, hyperlipidemia, stent type, length of stented segment, stent diameter and target vessel. In the second set of analysis, the relationship between genotypes and the outcome variable was tested. These analyses indicated that there were no statistically significant differences the three groups (χ2 (2) = 1.40, p=0 .47). The ACE D/D genotype or D allele does not influence the clinical and angiographic outcome of patients undergoing coronary stent placement. These data suggest that routine determination of the ACE genotype may not help identify patients who are at a higher risk of thrombotic and restenosis events after coronary stent placement.