Three recent U.S. Supreme Court antitrust rulings that influence the health-care delivery system are examined. Historically four defenses protected the health-care system from antitrust law. They are the learned-profession exemption, the fact that health-care systems have little effect on interstate commerce, the state-action defense, and the business-of-insurance exemption under the McCarran-Ferguson Act. These defenses and Supreme Court cases that have weakened or eliminated them are described. The cases are Arizona v. Maricopa County Medical Society, Union Labor Life Insurance Co. v. Pireno, and Blue Shield of Virginia v. McCready. Health-care providers will be subject to increased antitrust scrutiny as a result of these cases.