OBJECTIVES: Several studies show that adherence is an important factor to treatment success, improving patient outcomes and reducing global costs. The aim of this study is to estimate the clinical and economic impact of non-adherence by patients with ulcerative colitis in remission that are under maintenance treatment with mesalazine in the Brazilian Public Healthcare perspective. METHODS: We compared two schemes of Mesalazine 2 grams/per day: once daily (2 grams sachet) or twice daily (two 500 mg capsules q12). We constructed a decision tree analytical model to compare costs and outcomes of Mesalazine once daily (MOD) with Mesalazine twice daily (MTD) over 12 months. Treatment pathways described in the model are based on Brazilian Government Clinic and Therapeutics Guidelines, therefore, biological drugs were not considered in this analysis, because there are not reimbursed. In both arms, the failure to maintain remission led to other treatments, as needed: prednisone, cyclosporin, azatioprine and colectomy. Adherence data was obtained from real life prospective studies (Kane et. al.). Costs considered were: drug, laboratory and diagnostic tests’ costs, specialist consultation and hospitalization costs (all costs are referred to year 2011). The mains outcomes considered were colectomy surgery avoided and rates of remission without relapse. RESULTS: Results of the analysis suggest that the average aggregated treatment cost per person for all medical interventions at 12 months was lower for MOD compared with MTD (USD 1924 versus USD 1957). Additionally, there is a trend towards improved effectiveness with MOD in maintenance remission of ulcerative colitis with 6.6% re-inductions and 17.2% colectomy surgeries avoided.  CONCLUSIONS: Results from base-case and sensitivity analysis indicate that MOD presents lower costs and better effectiveness than MTD from a public payers’ perspective in Brazil.