 Abiraterone acetate is a steroidal irreversible inhibitor of CYP17 17α hydroxylaseC17, 20-lyase, blocking 2 important enzymatic activities in the synthesis of testosterone. The goal of this study is to compare the clinical benefit of abiraterone acetate plus prednisone with placebo plus prednisone in patients with metastatic castration-resistant prostate cancer CRPC who have failed one or two chemotherapy regimens, one of which contains docetaxel. All patients involved in the study will be randomized assigned by chance into one of two arms and will not know what study drug is being given to them. Study drug randomization allocation will be 2:1 abiraterone acetate: placebo. The study will be conducted in the United States, Canada, Australia, and the EU. The study will consist of screening, treatment, and follow-up. In this study, patients will receive study treatment abiraterone acetate or placebo plus prednisone until progression of clinical disease. Follow-up will continue until patient dies, is lost to follow-up, or withdraws informed consent. After providing written informed consent, patients will have screening procedures completed to determine eligibility. Safety evaluations at the screening procedure will include a physical examination, vital signs, and clinical blood laboratory tests, ECG, radiographs, urine tests, and recording of any adverse events including details of current prostate cancer symptoms. Patients will be asked to use a method of birth control with adequate barrier protection as determined to be acceptable by the principal investigator and sponsor during the study and for 13 weeks after last study drug administration. 