OBJECTIVES: Our goal was to analyze the rising utilization and to provide a comparison between expected number of patients and expenditures described in the submitted budget impact analysis and the real expenditures of mirabegron for treatment of overactive bladder since its introduction in the Czech Republic in January 2014. METHODS: The data source for our analysis was the business activity monitoring database of the General Health Insurance Company of the Czech Republic (VZP CR). VZP CR covers approximately 60 % of marketshare in the Czech Republic. Patient was defined as an insured person with a recorded prescription for mirabegron (G04BD12) during the observed period 01-12/2014. We identified the number of patients treated with mirabegron in the observed period and determined the real expenditures. We compared the real data with submitted BIA predictions. RESULTS: Since the introduction of mirabegron in January 2014 its utilization rose to 1.870 million DDD till 12/2014. There were 11 437 patients treated with mirabegron and the real expenditures of VZP CR representing 60% were €2.6 million (1EUR=27,24CZK) in 2014, which strongly differed from the predicted number of patients (2026) and expenditures (€672t-€1.mil) presented in the base case budget impact analysis in the reimbursement decision published by State Institute of Drug Control (SUKL). CONCLUSIONS: There was a significant difference between expenditures predicted in the submitted budget impact analysis and real expenditures. The real expenditures were almost 4 times higher than the base case predictions (2,5x higher when calculated with cost per patient estimation by SUKL) and more than 30% higher than the upper predictions for the first year. Expenditures in the first quarter 2015 (€1,5 million) have already reached the predictions for the whole 2015 according the base case. Further analysis will follow to confirm this trend.