PURPOSE: Acute aortic dissection (AAD) is considered one of the most common aortic catastrophes. However, there are a few epidemiological studies and true incidence was unknown in the general population. With the advent of newer diagnostic techniques, AAD is more frequently detected in radiological studies. We determined the incidence of AAD in a hospital patient group. METHODS: A hospital patient group was defined as all patients from the emergency room and outpatients' department (total number, 347,204) enrolled in Chungbuk National University Hospital between 2005 and 2010. Twenty-five AADs were detected by reviewing radiological reports (22,241 chest computed tomography [CT], 39,235 abdominal CT). A traumatic aortic dissection and isolated abdominal aortic dissection was excluded. We calculated person-years in all hospital patients and the incidence of AAD. We estimated a minimal general population based incidence by dividing a total population of geographical regions where patients of AAD were living. RESULTS: The annual age- and sex-adjusted hospital patients based incidence was 6.94 per 100,000 persons (95% confidence interval, 6.92 to 6.97). Nine dissections (36%) involved the ascending aorta, whereas sixteen (64%) involved the descending aorta. AAD was found in patients with six regions. A total population was 1,032,509 and patients included in the study were 296,505, in these six regions. An estimated minimal population based incidence was 1.99. CONCLUSION: In other studies, the incidence of AAD is approximately two to four per 100,000 persons per year. AAD in north area of Chungcheong, Korea occur with similar frequency when it is compared with other population based studies.