Although the incidence and prevalence rates of IBD in Korea are still lower than Western populations, they have been increasing rapidly during the past decades. Crohn's disease (CD) tends to run in families because it is thought to be related to genetic susceptibility coupled with environmental factors. A large number of monozygotic and dizygotic twin pairs with inflammatory bowel disease have been reported in western countries. The population relative risk in first-degree relatives is considered to be about equal in both Koreans and westerners. To our best knowledge, there is no report in monozygotic twins with CD in Korea. This case report is the first documented occurrence of concordant CD occurring in monozygotic twins in Korea.