With the advent of Medicare prospective payment systems, health care entities and physicians were forced to decrease expenses by sharing services and to increase revenue by attempting to jointly negotiate better reimbursement from third- party payers. Both activities have raised the specter of prosecution under antitrust laws that have been with us for more than a century but are poorly understood by practicing physicians. Recent monopolistic activities in the health care arena have prompted the Federal Trade Commission to file actions under specific acts of Congress, eg, the Sherman Anti-Trust Act, Clayton Act, Federal Trade Commission Act, Robinson-Patman Act, and Celler-Kefauver Act. Inasmuch as it is likely that specialties such as vascular surgery as a business will undergo substantial transformation, physicians need to be aware of the severe civil and criminal sanctions imposed if they are found guilty; fines that are several times actual damages; activities that raise antitrust issues including utilization review, medical staff privileges for competing specialties, participating provider agreements, and predatory pricing; and affirmative defenses and relief available in terms of specific exemptions. As health care providers react, innovate, and adjust to stay solvent, their business strategies will surely continue to be scrutinized for antitrust behavior by federal and state officials. The physician must have a basic understanding of the groundrules that govern any contemplated business strategy so that common pitfalls may be averted.