Background: With the rapid increase of robotic surgical systems in hospitals, it is important to understand the impact on treatment patterns for localized prostate cancer. The objective of this study is to determine whether the presence of robotic surgical systems independently influenced rates of surgery, radiation, and active surveillance for localized prostate cancer. Methods: We conducted an observational study using National Cancer Database (NCDB) state-level data, 2002-2010. Our study cohort includes patients newly diagnosed with clinical stage I-III prostate cancer from 48 states and Washington D.C. in the United States. The number of robotic systems installed in each state over time was obtained from publicly available information on-line. We characterized the state-level treatment pattern as the proportion of patients having surgery, radiation and active surveillance as their first course of treatment. Results: Between 2002 and 2010, the average number of robotic surgical systems per state increased from 2 to 26.3, while the unadjusted rate of surgery increased from 37.5% to 52.4%, radiation therapy decreased from 43.3% to 30.2%, and active surveillance increased from 7.0% to 9.3%. For every 10 additional robotic systems installed in a state, there would be a 2.5% increased rate of surgery (p<0.01), accompanied by a 1.3% (p=0.04) and 1.0% (p<0.01) decrease in the rate of radiation and active surveillance, respectively. Subgroup analyses suggest that the robotic adoption crowding out effect on radiation and active surveillance was driven primarily by men with stage I-II prostate cancer. If the adoption trajectory for robotic systems continues, the increased cost of treating localized prostate cancer in 2012 will be close to $27 million. Conclusions: During a period of rapid acquisition of robotic surgical systems, we found the number of robotic systems available at the state-level is significantly and directly associated with a higher rate of surgery for localized prostate cancer, and lower rates of radiation therapy and active surveillance.