Aim: This study has been performed on asthmatic patients in the Turkish population to determine the frequency of 4G/5G polymorphism genotypes of plasminogen activator inhibitor type-1 gene, and with the aim of examining the role of this polymorphism in asthma development. Methods: Genomic DNA obtained from 165 persons (98 patients with asthma and 67 healthy controls) was used in the study. DNA was multiplied with polymerase chain reaction using 4G and 5G allele-specific primers. Polymerase chain reaction products were assessed with CCD camera by being exposed to 2% agarose gel electrophoresis. Results were evaluated with chi-square test. Results: No statistically significant difference between the groups with respect to genotype distribution was found (p>0.05) in the study. The 4G allele frequency was indicated as 48% and 5G allele was as 52% in patients, whereas this was 50-50% in the control group. Conclusion: It has been established by this study that 4G/5G polymorphism genotypes of plasminogen activator inhibitor type-1 gene do not play a role in the development of asthma in the Turkish population.