The Sasang constitutional medicine classifies the mankind into four constitutional typesaccording to the individual psychological and physical traits. Differences in the Sasangconstitutional medicine may be explained by the genetic factors. In order to determine theassociation of Sasang constitutional classification and interleukin-1 receptor antagonist (IL-1Ra)in genetic susceptibility to ischemic stroke, we classified the four constitutional types in ischemicstroke patients (n=125) and the healthy control subjects (n=107), and genotyped for IL-1Rapolymorphism by polymerase chain reaction (PCR) methods. The distribution of the IL1RN*1/IL1RN*2 genotype in the ischemic stroke patients was significantly different from the healthycontrols (OR = 6.09; P =0.0134). And the prevalence of IL1RN*1/IL1RN*2 genotype was increasedin Taeum-in ischemic stroke patients, as compared to Taeum-in healthy controls (OR = 14.71; P =0.0144). These results suggest that IL1RN*1/IL1RN*2 genotype in Taeum-in might be associatedwith the increasing risk for ischemic stroke. Furthermore, this relationship could provide thebasis for a new approach in the investigation of the etiology of ischemic stroke.