OBJECTIVES: The Combination of Avodart®and Tamsulosin (CombAT) study shows that combination therapy provides a significantly greater degree of benefit than tamsulosin or dutasteride monotherapy in the treatment of moderate to severe benign prostatic hyperplasia (BPH). The objective of this study was to assess the cost-effectiveness of combination therapy with tamsulosin and dutasteride relative to either of monotherapies using recent information from the CombAT study. METHODS: A decision analytic model was constructed using a Markov model and a 1-year cycle time to estimate the clinical and cost consequences of tamsulosin, dutasteride, and combination therapy. Analyses were conducted for a 20-year time frame from the societal perspective. All costs are presented in 2009 US dollars, and costs and outcomes were discounted at a rate of 3% per year. Outcomes were expressed in terms of the incremental cost-effectiveness ratio (ICER), defined as the ratio of additional costs to additional QALYs. Sensitivity analyses were conducted on model probabilities, cost estimates, utility values and the discount rate. RESULTS: At both moderate and severe symptom levels, tamsulosin was dominated by dutasteride, that is, more costly and less effective than dutasteride. Compared to dutasteride, combination therapy was more expensive but more effective with the ICERs of $197,625 for moderate symptoms and $241,032 for severe symptoms. However, considering a societal cost-effectiveness threshold of $150,000 per QALY, combination therapy was not cost-effective compared to dutasteride. In most sensitivity analyses, these results were not sensitive to changes in model parameters. CONCLUSIONS: This study showed that tamsulosin was more costly and less effective than dutasteride, and the ICERs for combination therapy compared to dutasteride were higher than the cost-effectiveness threshold. Therefore, combination therapy is not cost-effective relative to dutasteride for moderate-to-severe BPH patients.