Ambulatory surgery centers (ASCs) are small (typically physician owned) healthcare facilities that specialize in performing outpatient surgeries and therefore compete against hospitals for patients. Physicians who own ASCs could treat their most profitable patients at their ASCs and less profitable patients at hospitals. This paper asks if the profitability of an outpatient surgery impacts where a physician performs the surgery. Using a sample of Medicare patients from the National Survey of Ambulatory Surgery, we find that higher profit surgeries do have a higher probability of being performed at an ASC compared to a hospital. After controlling for surgery type, a 10% increase in a surgery's profitability is associated with a 1.2 to 1.4 percentage point increase in the probability the surgery is performed at an ASC. Copyright © 2010 John Wiley & Sons, Ltd.