Project Summary and Relevance Many men diagnosed with prostate cancer will not die of it even without any intervention, enhancing the possibility of overtreatment. How urologists organize themselves is strongly linked to the nature and extent of treatment for localized prostate cancer. Those practicing in large urology groups, particularly urologists with an ownership stake in radiation facilities, more commonly treat men with prostate cancer who are unlikely to benefit (i.e., overtreatment). Conversely, urologists in multispecialty groups provide care at a lower cost, without compromising quality. Uncertainty surrounding the implications of evolving health policy is prompting a sea change in how physicians align themselves. Faced with increasing administrative burden to navigate reforms, urologists practicing alone or in small groups are aligning themselves with larger entities, including multispecialty groups and large urology groups. Because practice context is strongly tied to prostate cancer overtreatment and spending, policy induced realignment of urologists has significant public health implications. The goal of this national study is to understand the effects of policy on relationships between urologist practice organization and prostate cancer care (i.e., treatment, quality and payment). This grant, which uses national Medicare data, has the following three aims: 1) To determine the effect of changing practice organization on prostate cancer care; 2) To measure the effect of hospital ownership of urology practices on prostate cancer care; and, 3) To determine how policy impacts relationships between urologist practice organization and prostate cancer care. We plan to use interrupted time series and difference-in-difference methods to control for differences in baseline case-mix and temporal trends. Results from this study have real-world implications for patients, who are naturally interested in getting the best prostate cancer care at the lowest possible cost. Our findings will immediately inform policymakers on the extent to which the impact of policy is mediated by practice organization, particularly by those that have historically favored volume over value.