OBJECTIVES: To estimate the budget impact (BI) of adding a new fixed-dose combination (FDC)  of 0.5mg dutasteride and 0.4mg tamsulosin daily to the Regie de L’assurance Maladie du Quebec (RAMQ) formulary for a three year period following its listing for the treatment of symptomatic benign prostatic hyperplasia (BPH) METHODS: The analysis compared RAMQ drug expenditures after the introduction of FDC (New Drug Scenario) with an alternative scenario without FDC (Reference Scenario). Treatments in the reference scenario include alpha blockers (tamsulosin, doxazosin, terazosin, alfuzosin), 5α-reductase inhibitors (finasteride, dutasteride) and their combinations. The treated population was assumed to be equal to the population of men in Quebec aged ≥50 years with moderate to severe symptoms of BPH (estimated at 312,448). In the primary analysis, FDC was assumed to gain 2.5%, 5.8% and 9.3% of BPH market share in the first 3 years after listing with 75% of share gains coming from patients switching from an alpha blocker plus dutasteride, and 25% from patients switching from tamsulosin monotherapy. One-way sensitivity analysis was performed to quantify the effect of uncertainty around the market shares assumptions. RESULTS: In the primary analysis, adding FDC to RAMQ is projected to result in a cost saving of $0.253M over three years.  Assuming only 60% of market share comes from patients currently taking dutasteride plus an alpha blocker, the total incremental BI is $5.879M over 3 years. If FDC gains 90% of its market shares from dutasteride plus an alpha blocker, the BI would results in a cost saving of $6.386M over 3 years. CONCLUSIONS: Based on this budget impact analysis, it may be cost-saving for the RAMQ to switch patients who are treated with combination therapy of separate drugs of dutasteride and an alpha blocker to a FDC of dutasteride and tamsulosin.