One year of graduate medical education, the internship, had become the norm for graduates of most U.S. medical schools by 1920, and subsequently was adopted by most states as a criterion for licensure. The original concept of a "resident physician" carried with it responsibility for patients 24 hours per day, seven days per week. Recent public and media attention to the issues of residents' supervision and working hours has led to governmental efforts to restrict their hours and set minimum requirements for supervision. New York is the first state to impose specific requirements. The New York recommendations have implications for the concept of graded responsibility for residents, for learning the natural course of illness, and for the need to provide service in hospitals. Further, the recommendations raise four objections: they do not recognize differences by type of specialty or year of training; they might affect the length of time needed to acquire aggregate clinical skills; they affect different types of hospitals differently; and they would have a major effect on physician manpower. Hospitals and residency programs will face several difficult choices in responding to the regulations. To provide its members with guidelines for action, the Executive Council of the Association of American Medical Colleges has issued recommendations for residency hours and supervision, including the use of an 80-hour work-week averaged over four weeks, the continued use of graded supervision of residents in emergency rooms and in inpatient and ambulatory settings, and control of housestaff moonlighting.