OBJECTIVES: Costs for the population of metastatic castrate-resistant prostate cancer (mCRPC) patients can be difficult to discern due to the lack of a specific International Classification of Diseases, 9th Revision (ICD-9) code. This study described the resource utilization and costs of patients with mCRPC in a large US health claims database using chemotherapy administration as a proxy. METHODS: Data from January 1, 2006-June 30, 2011 from the MarketScan Commercial and Medicare databases were used in this analysis.  Index date was defined as the first docetaxel, mitoxantrone, estramustine, vinorelbine, cabazitaxel or abiraterone treatment date between January 1, 2007 and June 30, 2010.  Additional inclusion criteria: >=18 years old; continuous pharmaceutical and medical enrollment >=6 months prior to and >=2 months following the index date; >=1 ICD-9 diagnosis code for prostate cancer (185.x).  mCRPC related costs were identified by the presence of an ICD-9 code of 185.x on the claim.  Costs were estimated separately for chemotherapy, radiation, inpatient, outpatient and emergency room (ER). Median per patient per month (PPPM) costs were calculated at the patient level. RESULTS: 4,005 patients were eligible, with a mean age of 70.2 years.  For patients with medical utilization, total median PPPM costs increased from $3,107 pre-index to $6,939 post-index. Chemotherapy costs increased ($234 pre-index vs. $1,439 post-index), while radiation costs decreased ($793 vs. $394).  Excluding costs related to chemotherapy, radiation and other drug treatment, costs for inpatient, outpatient and ER visits increased from $2,120 pre-index to $4,388 post-index.  Both mCRPC-related costs ($862 vs. $1,986) and non-mCRPC-related costs ($763 vs. $1,628) rose. CONCLUSIONS: These findings indicate that the cost burden from mCRPC is quite large.  With aging of the population, prevalence of prostate cancer is expected to increase to 3.2 million in the US by 2020 with costs continuing to escalate. Further research is needed to understand these cost implications, especially for the Medicare system.