The Sasang constitutional medicine classifies the mankind into four constitutional types according to the individual psychological and physical traits. Differences in the Sasang constitutional medicine may be explained by the genetic factors. In order to determine the association of Sasang constitutional classification and interleukin-1 receptor antagonist (IL-1Ra) in genetic susceptibility to ischemic stroke, we classified the four constitutional types in ischemic stroke patients (n = 125) and the healthy control subjects (n = 107), and genotyped for IL-1Ra polymorphism 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 healthy controls (OR = 6.09; P =0.0134). And the prevalence of $IL1RN^*1/IL1RN^*2$ genotype was increased in 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 associated with the increasing risk for ischemic stroke. Furthermore, this relationship could provide the basis for a new approach in the investigation of the etiology of ischemic stroke.