We systematically reviewed and compared the efficacy and safety of once daily (OD) mesalamine to conventional dosing for induction and maintenance of remission in ulcerative colitis (UC). A literature search to January 2012 identified all applicable randomized trials. Study quality was evaluated using the Cochrane risk of bias tool. The GRADE criteria were used to assess the overall quality of the evidence. Studies were subgrouped by formulation for meta-analysis. Eleven studies that evaluated 4070 patients were identified. The risk of bias was low for most factors, although five studies were single-blind and one was open-label. No difference was observed between the dosing strategies in the proportion of patients with clinical remission (relative risk [RR] 0.95; 95% confidence interval [CI] 0.82-1.10), clinical improvement (RR 0.87 95% CI 0.68-1.10), or relapse at 6 (RR 1.10; 95% CI 0.83-1.46) or 12 months (RR 0.92; 95% CI 0.83-1.03). Subgroup analyses showed no important differences in efficacy. No significant difference was demonstrated in rates of medication adherence or adverse events between OD and conventional dosing. OD mesalamine appears to be as effective and safe as conventional dosing for both the treatment of mild to moderately active UC and for maintenance of remission in quiescent UC. The failure to demonstrate a superior rate of adherence to OD dosing may be due to the high rate of adherence observed in the clinical trials environment. Future research should assess the value of OD dosing in community settings.