Background: Dosing frequency is an important treatment consideration that has been shown to influence adherence and outcomes when treating ulcerative colitis (UC). In this analysis we evaluate the economic consequences of outcome differences observed in the study comparing mesalazine 4g per day once daily (OD) versus 4g per day in twice daily (BD) doses in combination with 1g mesalazine enema in patients with active ulcerative colitis (MOTUS). Methods: Cost-effectiveness analysis comparing costs and outcomes based on data obtained from the multicenter, randomized, controlled MOTUS trial were used. Medical costs were based on treatment guidelines in the Netherlands and applying published cost data to resources consumed. Outcomes generated in the model were quality-adjusted life years (QALYs) based on active UC health state utilities derived from ulcerative disease activity index (UCDAI) and changes in active UC status. The defined health states based on accepted treatment practices applied in the Markov model were as follows: (1) active UC with 4g mesalazine (OD or BD); (2) mesalazinerefractory active UC; (3) steroid-refractory active UC; (4) infliximab-responsive active UC; and (5) remission. The health service perspective of the Netherlands was reflected in the model and considered a 32 week time horizon with 4 weekly Markov cycles. Results: After 32 weeks the mean per patient costs were € 2,943 and € 3,444 for those treated with OD and BD mesalazine, respectively, with an average per person savings of € 501 per patient treated with OD. Within 8 weeks 82% and 78% of patients achieved remission in the OD and BD cycles. At 32 weeks the accumulated QALYs were 0.57 and 0.56 for OD and BD mesalazine, respectively, resulting in a cost per QALY of € 5,518 and € 6,485, respectively. Mesalazine treatment costs, including 4 g mesalazine for maintenance and 2 g mesalazine for those that achieve remission represented 23% (€ 668) and 20% (€ 680) of all treatment costs. Conclusions: The OD daily dosing regimen was found to be cost-saving compared with BD dosing in active UC. The major cost driver for achieving remission was ancillary treatment escalation costs which included intravenous prednisolone and high cost biological agents. The precise mechanism why OD may improve outcomes is undetermined. However, the team posits that the OD dosing could lead to higher peak luminal concentration and higher mucosal concentration of mesalazine compared with divided dosing with similar daily dose.