OBJECTIVES: Patients diagnosed with metastatic (M1) prostate cancer (PCa) are predisposed to skeletal related events (SREs), including bone surgery (BS), pathologic fracture (PF) and spinal cord compression (SCC). There is limited information regarding the change in costs associated with SREs, by type, among stage IV M1 PCa patients.  METHODS: We analyzed patients aged 66+ with an (AJCC) M1 PCa diagnosis. Cases diagnosed between 2000 and 2007 were identified from the Surveillance, Epidemiology, and End Results (SEER)-Medicare dataset.  Patients were followed until death or censoring. Incremental costs per patient were calculated for the 12-month pre-period and the 12-month post-period relative to the first post-diagnosis SRE.   Results were reported as the average percent change in the total pre-post period costs. Subgroup analysis was carried out separately for individuals who survived (survivors) and died (non-survivors) within the 12-month post-period. A sensitivity analysis was carried out for a 6-month pre-post interval. The analysis was conducted from a US Medicare system perspective.   RESULTS: Application of inclusion criteria resulted in 1,234 stage IV M1, PCa patients with SREs. The average age was 78 years and 11% were African American. Five, mutually exclusive SRE groups were evaluated: PF-only (n=180), SCC-only (n=634), BS-only (n=200), PF with BS (n=163), SCC with BS (n=57). The average percent increase in the total costs in the post-period compared to the pre-period was 67%. The average percent increases in costs for each of the subgroups were as follows: PF-only, 53%; PF with BS, 71%; SCC-only, 64%; SCC with BS, 88%; and BS-only, 70%.  Subgroup analysis showed a 77% increase in total costs among survivors and a 60% increase in costs among non-survivors.  The average percent increase in SRE costs using a pre-post period of 6 months was 75%.     CONCLUSIONS: The percentage increase in costs post-SRE varies by type of SRE, survival post-SRE, and interval length.