BACKGROUND AND OBJECTIVES: Platelets play an important role in the pathogenesis of acute coronary syndrome. Prostacyclin inhibits platelet aggregation, smooth muscle cell proliferation and vasoconstriction, and it counteracts thromboxane A2 activity. The purpose of this study is to evaluate the association between a single nucleotide polymorphism in the prostacyclin synthase gene and myocardial infarction in Koreans. SUBJECTS AND METHODS: We studied total 119 patients (M: F=72: 47, mean ages=57.9). We compared 60 acute coronary syndrome patients who underwent coronary angiography with the diagnosis of acute myocardial infarction (MI), with 59 normal control group patients who had normal coronary angiograms. With the use of polymerase chain reaction-restriction fragment length polymorphism analysis, we identified a single nucleotide polymorphism, C1117A, in exon 8. RESULTS: The genotype distribution and allele frequencies were significantly different between the control group and MI group. Frequency of the genotype C1117A was: AA: AC: CC=3.4%: 30.5%: 66.1% in control group, respectively, and AA: AC: CC=1.7%: 10.0%: 88.3% in MI group, respectively. Prostacyclin synthase polymorphism was observed in the MI group and the control group, but the frequency of the CC genotype was high in MI group (odds ratio, 3.88; 95% CI 1.49-10.88, p=0.003). Compared to control group, being male, having diabetes, hypertension or obesity, and the smoking rate were high in MI group. There were not significantly differences between genotypes for clinical characteristics. CONCLUSION: We conclude that the C1117A polymorphism in exon 8 of the prostacyclin synthase gene is associated with MI, and it may be a genetic marker of MI in Koreans.