Introduction: Inflammatory Bowel Disease (lBD), including crohn's disease (CD) and ulcerative colitis (UC), belong to the group of inflammatory disease with unknown origin, which primarily involve the gastrointestinal tract but also have extra intestinal manifestations. In western studies, an annual incidence of 5-11 in a hundred is thousand's estimated and no similar epidemiological studies have been performed so far in Iran. In this study our goal is to determine the pattern of IBD and it's clinical aspects in Arak.Material and Methods: In this study of 20 months duration (from April 2000 to Sep 2001), all the patients with suspected IBD, referred to specific clinics, were evaluated by careful clinical, para-clinical, colonoscopy and histo-pathological tests and finally the diagnosis of IBD was made according to these criteria and then the collected data was statistically analyzed.Results: From the total number of 108 patients, diagnosed with IBD, 97 cases (89.8%) had UC and (10.2%) had CD. From the patients with UC, 41 (47.4%) were female and 21 (52.6%) were male and in CD patients, 8 cases (72.7%) were female and 27.3% male. 58.8% of UC cases were under 40 years of age, in 19 cases (19.6%) of patients with UC, the duration of the disease was less than a year. Rectal involvement existed in all the patients with UC. Extra-intestinal manifestations were rare except anemia. Patients with CD were all under 30 years old and ileocecal involvement existed in 8 of them with major manifestations of mal-absorption syndromes. Recurrent fistulas led to 2 deaths.Conclusions: Although this is not a broad epidemiologic study, our effort was to detect the maximum number of patients with IBD and in regard with 19 cases with less than a year history of the disease, the annual incidence, of IBD, in Arak is estimated to be more than %3.04 in hundred thousand in the UC from of IBD, less complications (cancer, stenosis and toxic colon) were found in comparison to western studies and in the case of CD, the prevalence is much lower but is accompanied by more serious GI complications. It is likely that IBD is no less prevalent in this region than the west but it is more missed and undetected which can be resolved by better evaluation of the patients upon admission.