Study objectives: There are about 10 known thrombosis genes that are considered to be an important risk factor for the occurrence of ischemic stroke. Recently, the polymorphism of the β-fibrinogen G/A-455, the rate-limiting region of the blood coagulation cascade, has been reported to be associated with the development of ischemic stroke. The aim of this study is to determine the relationship between the β-fibrinogen G/A-455 single nucleotide polymorphisms and the risk of ischemic stroke in Korea because there are racial differences in polymorphisms and Koreans have never been studied before. Methods: From March to September 2003, we compared 96 (male:female=1.2:0.8) patients who were diagnosed with ischemic stroke at the Kyung Hee University hospital emergency department and 129 control subjects, men or women, between the ages of 50 and 70 years. The genotypes of β-fibrinogen G/A-455 polymorphisms were confirmed by polymerase chain reaction followed by Hae III restriction enzyme digestion. The ischemic stroke patients were divided into 3 groups (large-vessel disease, lacuna stroke, and other reasons [unknown, aortic dissection]) by computed tomography and magnetic resonance imaging diagnosis by a radiologist. They were compared, and the statistics were done using 1-sample t test, χ 2 test, and analyses of variance, and the statistical significance was defined as P value less than .05. Results: The results showed that the patient group had a much higher rate of heterozygotism (GA or AG). We analyzed the genotype frequency of 80 patients, and the percentage of homozygote of the cut type (GG type) was 58.7%, and the uncut type (AA type) was 7.5%, whereas the control group showed 73.3% of the uncut type and 2.7% of the cut type. For allele frequency in the patient group, A allele was 81.3% and G allele was 18.7% in comparison with that of the control group, which was 85.3% for A allele and 14.7% for G allele. The analysis of the statistics of genome frequency showed χ 2 to be 6.24, resulting in a significant difference between the patient and the control group ( P 2 was 1.88 (95% confidence interval 1.16 to 3.04; P Conclusion: The high rate of polymorphisms of AA genotype of β-fibrinogen G/A-455 in large-vessel atherosclerosis of cerebrovascular disease in Koreans leads us to believe that the prognosis of men with β-fibrinogen G/A-455 AA–type polymorphism and a smoking history, if these were found in advance, could be improved by early diagnosis and preventive management, and clinical expenses could be reduced.