OBJECTIVES: Non-adherence with oral mesalazines has a significant impact on treatment outcome which is one of the most important predictors for relapse in ulcerative colitis. The objective of this study was to assess adherence and persistence with oral mesalazines, particularly to analyze whether adherence with oral mesalazines is linked to the use of once daily high strength Mezavant® compared to more frequent dosing and/or low strength oral mesalazines. METHODS: A retrospective prescription claims analysis of a random sample of patients from the Quebec provincial public health plan (RAMQ) database was conducted. New users of a mesalazine formulation during the period from January 2005 to December 2009 and with no diagnosis of Crohn’s disease were eligible for inclusion in the analysis. Treatment adherence was estimated using medication possession ratio over a one-year period. For the analysis of persistence to treatment, patients were considered non-persistent if they had not used the mesalazines medication for a period of twice the median duration of prescriptions. Proportion of patients who were persistent was estimated at 3-, 6-, and 12 months after index prescription. RESULTS: The mean age of the study sample was 55.7 years (SD = 18.2) and the proportion of males and female were similar (48.8% vs. 51.2%). The proportion of patients ≥80% compliant on the mesalazine long acting formulation (Mezavant®) (46.3%) was significantly higher compared with all other mesalazine formulations (1.6% to 26.0%) (p<0.001). The proportion of patients who were persistent at 12 months on Mezavant® (70.2%) was higher when compared with those on any other mesalazine formulations (14.5% to 42.6%) (p<0.001).  Similar trends were observed at all time points examined. CONCLUSIONS: Results of these prescription claims analyses indicate that adherence and persistence to mesalazine formulations are relatively poor, however improved adherence and persistence are observed with the long acting formulation (Mezavant®).