The relationship between physicians and nurses in the delivery of anesthesia care is politically and financially charged, and hotly debated. Against this backdrop, federal regulators have proposed dropping a Medicare requirement that nurse anesthetists be supervised by a physician. Proponents note that the new regulations would resolve inconsistencies between Medicare supervisory requirements and state law, while opponents voice concerns for patient safety. This Issue Brief describes the current controversy, and summarizes a newly published study that suggests differences in patient outcomes depending on the nature and level of anesthesiologist involvement in surgical care.