OBJECTIVES: Highly effective biologic therapies offer new treatment options for patients suffering from moderate to severe ulcerative colitis (UC) who fail with conventional therapies. A budget impact model was constructed to estimate the costs of infliximab therapy for steroid-dependent, steroid-refractory and acute UC patients in the perspective of Croatia. METHODS: Using epidemiology data and medical treatment guidelines, a budget impact model was constructed to calculate the annual cost of infliximab according to the Croatian Guidelines for Treatment of UC. Moderate to severe UC patients that were diagnosed steroid-dependent, and acute or steroid-refractory patients that were non-responsive to IV corticosteroids were considered eligible for infliximab. Clinical trial data was applied to the guidelines to determine infliximab eligible patients. Sensitivity analysis was conducted to describe the ranges of costs by varying incidence, and dosing, considering drug wastage. RESULTS: According to the epidemiology data, 17.8% (411 patients) of all UC patients fall into these 3 categories of patients and should be treated with infliximab. Total costs of treating these patients according to drafted guidelines would be 33,822,366 kn (0.01% of GDP, 0.13% of total healthcare costs or 0.50% of total pharmaceutical sales for 2010), 19,329,407 kn (57.15%) of which is attributed to steroid-dependent patients, 7,893,089 kn (23.34%) to steroid-refractory and 6,599,870 kn (19.51%) to acute patients. New patients who require 8 infusions within the first year account for 11% of the cost, whereas maintenance therapy patients receiving 6 infusions explain the rest. Adjusting the dosage from 400mg/kg to 350mg/kg decreases the total cost by 12.50% (4,227,796 kn). A decreasing incidence of UC patients from 5.9 to 3.9 per 100,000 reduces the cost by 4.69% (1,586,046 kn). CONCLUSIONS: Given the significant improvement in quality of life of those with UC, infliximab should be considered where the budget allows it. Steroid-refractory UC patients accounted for majority of the costs.