The purpose of this study is to evaluate the incidence, prevalence, clinical characteristics and prognosis of Crohn's disease and ulcerative colitis over time in a district of Seoul, Korea.

Inflammatory bowel disease (IBD), which is comprised of Crohn's disease (CD) and ulcerative colitis (UC) is a chronic inflammatory disease of gut with uncertain etiopathogenesis. According to our previous study (Yang, et al. Inflamm Bowel Dis 2008; 14: 542-549), the incidence and prevalence of IBD in Korea are still low compared with those in Western countries, but are rapidly increasing. However, the long-term trends of epidemiology of CD and UC together with their characteristics and prognosis in Korea are uncertain yet. The investigators therefore aim to elucidate the incidence and prevalence of CD and UC over a 30-year period, from 1986 to 2017, in the Songpa-Kangdong district of Seoul, Korea. In addition, the investigators also aim to reveal the clinical features at the time of diagnosis of IBD, long-term evolution of disease and prognosis.

Inclusion Criteria:

• Definite cases of CD and UC

Patients are diagnosed with CD if they meet at least 2 of the following criteria:

1. clinical history of abdominal pain, weight loss, malaise, diarrhea, and/or rectal bleeding
2. endoscopic findings of mucosal cobblestoning, linear ulceration, skip areas, or perianal disease
3. radiologic findings of stricture, fistula, mucosal cobblestoning, or ulceration
4. macroscopic appearance of bowel wall induration, mesenteric lymphadenopathy, and "creeping fat" at laparotomy
5. pathologic findings of transmural inflammation and/or epithelioid granulomas

Only patients who meet these criteria for at least 2 months are included.

Patients are diagnosed with UC only if all 3 of the following criteria are present

1. a typical history of diarrhea or blood and pus or both in the stool for longer than 4 weeks
2. a typical sigmoidoscopic or colonoscopic picture with diffusely granular, friable, or ulcerated mucosa without rectal sparing or skip lesions or radiological signs of characteristic continuous granular or ulcerated mucosa
3. characteristic histopathological signs of inflammation on biopsy

Exclusion Criteria:

• IBD unclassified
• Ethnic groups other than Korean

The study is performed in the Songpa-Kangdong district, a well-defined administrative area in Seoul, the capital of Korea, beginning in 1986, when the first patient with IBD was diagnosed, until 2017. The population of the study area was racially and ethnically homogeneous and was relatively stable in number.