Objective: Ulcerative colitis (UC) is a chronic condition that afflicts young adults in their economically productive years. Because of its long duration, UC causes high use of health services and high lifetime costs for medical care. The aim of this study was to measure the annual costs of patients with UC from the Brazilian public heath perspective and to identify potentially relevant determinants of costs Methods: Thirty-one gastroenterologists from southeast Brazil prospectively evaluated all their UC patients during two months. They used a structured questionnaire specifically developed to evaluate resource use by patients with ulcerative colitis. Costs of medical services (diagnostics and treatment) were considered as well as costs of medication. Resource use was valued using government reimbursement for hospital services and government tender prices drugs. Results: A total of 175 patients were evaluated. The mean annual cost of one CD patient was R$1945.06, including medication, physician, laboratory, diagnostic, hospitalization and surgery costs. Medication, hospitalization, surgery and diagnostic procedures accounted respectively for 95%, 3%, 1%, and 1% of the total annual costs. Mesalazine was the most used drug to initiate UC`s treatment (58%). There was no statistical difference between the costs of the patients treated with mesalazine and sulfasalazine. Due to differences in the mean dosage of theses drugs, mesalazine daily cost is lower than sulfasalazine Conclusion: This is the first time that UC treatment costs have been demonstrated from the Brazilian public health perspective. Although mesalazine is deemed to be more expensive than sulfasalazine and considering that there was no statistical difference in total costs among patients taking mesalazine and sulfasalazine, and that medications represent more than 90% of total UC treatment annual costs in the public Brazilian health care system, the use of mesalazine may represent a reduction factor in the financial resource expenditure for the treatment of UC