Background: Despite claims of rarity, some studies indicate that the prevalence of inflammatory bowel disease has increased in Iran during the past decades. Establishment of a registry and the clinical characteristics are presented in this study.Methods: Two hundred ninety-three patients with ulcerative colitis and 207 with Crohn's disease, referred to tertiary referral gastrointestinal centers in Tehran from 2004 through 2007, were assessed. Demographic and clinical features, intestinal and extraintestinal manifestations, inflammatory bowel disease in relatives, measles infection and vaccination, nutrition during infancy, and drugs and surgical interventions were assessed.Results: The mean+/-SD age at the diagnosis was 33.8+/-12.9 years in Crohn's disease and 37.1+/-13.7 years in ulcerative colitis. Male:female ratio was 0.9:1.0 for Crohn's disease and 0.7:1.0 for ulcerative colitis. A total of 177 (85.5%) patients with Crohn's disease, and 254 (86.7%) patients with ulcerative colitis had never smoked. Measles vaccination was mentioned in 150 (72.5%) of Crohn's disease and 214 (73%) of ulcerative colitis patients. Breastfeeding during infancy was reported in 178 (86%) and 257 (87.7%) of Crohn's disease and ulcerative colitis patients, respectively. Appendectomy was reported in 37 (17.9%) of Crohn's disease and 16 (5.5%) of ulcerative colitis patients, whereas tonsillectomy was reported in 11.6% of each group.Conclusion: Demographic and clinical characteristics of inflammatory bowel disease patients are similar to that of other developing countries, in this study, more inflammatory bowel disease cases have been assessed in comparison with previous studies, which may be due to different time scales of socioeconomic evolution and environmental factors in Iran.