Purpose: National attention has focused on whether urology-radiation oncology practice integration � known as integrated prostate cancer centers (IPCCs) � contributes to use of intensity-modulated radiation therapy (IMRT), a common and expensive treatment for prostate cancer. Methods: We examined prostate cancer treatment patterns pre- and post-conversion of a urology practice to an IPCC in July, 2006. Using the SEER-Medicare database, we identified patients age ? 65 years diagnosed in one state-wide registry with non-metastatic prostate cancer between 2004 and 2007 and classified patients into 3 groups: (1) those seen by IPCC physicians (exposure group); (2) those living in the same hospital referral region (HRR) and not seen by IPCC physicians (HRR-control group); and (3) those living elsewhere in the state (state-control group). We compared changes in treatment among the 3 groups, adjusting for patient, clinical, and socio-economic factors. Results: Compared with the 8.1 percentage point (ppt) increase in adjusted IMRT use in the state-control group, IMRT increased 20.3 ppts (95% confidence interval [CI] 13.4, 27.1) in the IPCC group and 19.2 ppts (95% CI 9.6, 28.9) in the HRR-control group. Androgen-deprivation therapy (ADT), for which Medicare reimbursement declined sharply, decreased similarly in the IPCC and HRR-control groups. Prostatectomy declined significantly in the IPCC group. Conclusions: Coincident with the conversion of a urology group practice to an IPCC, we observed increases in IMRT and decreases in ADT among patients seen by IPCC physicians and those seen in the surrounding healthcare market that were not observed in the remainder of the state.