During training, doctors often work long hours and are “on call” (working through the night in the hospital) every few days. Over the past decade, concern about bad effects of these long working hours on patient care has increased. Regulations that limit working hours for doctors in training to 80 hours per week have been in effect in New York since the late 1980s. In July 2003, rules went into effect throughout the United States to restrict the number of hours that doctors in training can work. However, whether restriction of work hours is associated with better patient outcomes is unclear. Doctors who are well rested may be less likely to make errors than doctors who are tired. However, the increase in transfers of patients from one doctor to the next that results from decreasing work hours could make errors more likely.