Background: Abiraterone acetate, an androgen biosynthesis inhibitor, received FDA approval in 2011 for metastatic castration-resistant prostate cancer (mCRPC) patients who have received prior chemotherapy containing docetaxel., Objective: To estimate the projected budgetary impact of adopting abiraterone for mCRPC patients from a U.S. health plan perspective., Methods: A decision analytic model compared mCRPC treatment cost before and after abiraterone acetate adoption based on a hypothetical 1,000,000-member plan. Plan mCRPC prevalence was derived from prostate cancer incidence reported in U.S. epidemiology statistics and disease progression data from published trials. Market shares for comparator mCRPC treatments (prednisone alone; cabazitaxel + prednisone; mitoxantrone + prednisone; docetaxel retreatment + prednisone) were derived from market research simulation. Abiraterone + prednisone uptake (8% - scenario 1 to 55% - scenario 3) was based on assumptions for illustrative purposes. Treatment costs were computed using prescribing information, treatment duration from phase III trials, and drug costs considering common U.S. cost listing and reimbursement schemes. Prevalence and costs of managing treatment-related toxicities were estimated from literature, treatment guidelines, and expert clinical opinion. The model evaluated the perspectives of a commercial payer with no Medicare beneficiaries and a commercial payer with a subset of Medicare beneficiaries. Sensitivity analyses were conducted to assess changing input values., Results: In each modeled scenario, 57 patients with prior docetaxel therapy received treatment for mCRPC. For the commercial perspective, the incremental per-member-per-month (PMPM) cost attributable to abiraterone ranged from $0.0019 in scenario 1 to $0.0133 in scenario 3. For the commercial/Medicare perspective, the incremental PMPM ranged from $0.0026 in scenario 1 to $0.0176 in scenario 3. The average incremental PMPM cost over 3 scenarios is $0.0112. When testing key sensitivity scenarios, the model indicated that abiraterone treatment duration and cabazitaxel market share were the main drivers of cost., Conclusions: The model results indicate that reimbursement for abiraterone may have a neutral impact on a U.S. health plan budget given the relatively small size of the eligible prostate cancer population and expected lower toxicity-related costs as compared with chemotherapy. The sensitivity analyses addressing the components of uncertainty in the model show that the budgetary impact of abiraterone is likely low.