Asthma is considered as a chronic inflammatory airway disease and defined as increased tracheobronchial responsiveness to variety of stimuli. Edema and inflammatory cell infiltration in airway is observed in the asthmatic patients. One of the essential changes in inflammation is adhesion of leukocyte to endothelium and transmigration of leukocytes to the sites of inflammation. Unfortunately, little is known about the role of platelet endothelial cell adhesion molecule-1 (PECAM-1) polymorphism in asthma inflammatory process. The purpose of this study was to determine whether PECAM-1 polymorphisms affect the risk of asthma or not.Forty-five asthmatic patients (including 27 men and 18 women) and 45 healthy volunteers (11 men and 34 women) were studied. To determine the severity of the asthmas situation, a questionnaire was prepared asking the following information: age, sex, clinical signs and symptoms and past medical history. All subjects were genotyped for PECAM-1 polymorphism by using amplification refractory mutation system -polymerase chain reaction (ARMS-PCR). The genotype distribution of PECAM-1 80 Val/Met polymorphism in all asthmatic patients were Val/Val while non asthmatic controls were 95.6% Val/Val and 4.4% Val/Met. However, these differences were not statistically significant (p<0.05). The allele and genotype frequencies of PECAM-1 125 Val/Leu polymorphism were significantly different between asthmatic patients and controls. On the other hand, the presence of 125 Leu allele was associated with an increasing risk of asthma with an odds ratio of 2.8 (95% CI; 1.5-5.3, p=0.002). Our findings suggest that the PECAM-1 125 Val/leu polymorphism might be a genetic factor that may be associated with asthma.