6527 Background: Men with prostate cancer have a variety of treatment options, including surgery, radiation, hormonal therapy, combinations thereof, or active surveillance. Treatment choice may have important cost implications. Methods: Using the SEER-Medicare database, we examined the Inpatient, Outpatient, Emergency, and Other costs of men diagnosed with local/regional prostate cancer in the year 2000 who were 66+ years old and enrolled in the fee-for-service Medicare program. Based on the treatments received in the first 9 months from diagnosis, men were assigned to these treatment groups: active surveillance, radiation, hormonal, hormonal+radiation, surgery (might also include radiation and hormonal therapy). We matched the prostate cancer cases to noncancer controls on age, race, sex, SEER region, comorbidity, and survival. We estimated the costs of prostate cancer care from 1 month pre- to 12 months post-diagnosis by calculating the incremental costs of care for cases vs. controls. Costs of care were estimated using Medicare payments. Results: 13,769 prostate cancer cases were matched with 13,769 controls and allocated to these treatment groups: active surveillance (n=2,805), radiation (n=2,582), hormonal (n=2,190), hormonal+radiation (n=3,992), and surgery (n=2,200). The most expensive treatment group was hormonal+radiation, with cases having a total average incremental cost of $17,795 vs. controls, followed by surgery ($15,467), radiation ($12,326), and hormonal therapy ($10,804). Active surveillance was the least expensive ($4,152). Outpatient costs were the major driver of increased costs for the hormonal+radiation group. Increased costs for surgery patients were driven by both Outpatient and Inpatient costs. Emergency Department and Other costs were generally similar between prostate cancer cases and controls. Conclusions: The treatment choice of men with local/regional prostate cancer has important implications for cost in the year following diagnosis. Additional analyses exploring long-term costs are needed. [Table: see text] No significant financial relationships to disclose.