In 2003, the Accreditation Council for Graduate Medical Education (ACGME) implemented a single duty-hour standard nationwide. The evidence to date suggests that this neither improved nor worsened patient outcomes. In June 2010, the ACGME proposed a new set of duty-hour standards for implementation in July 2011. The main disadvantage of this approach is that there is no ability to determine whether different standards would have worked better to reduce resident fatigue while improving patient safety. Many unanswered questions remain about how to design duty-hour standards, but relatively little evidence exists. In addition, the same approach may not work in all specialties and all hospitals. A more flexible, dynamic policy that emphasizes ongoing testing and evaluation would be more likely to achieve improvements in clinical and educational outcomes.