Since implementation of the mandate for restrictions in trainee work hours in 2003, debate surrounds its impact on patient safety. An early study suggested that the change reduced serious medical errors, but the cost implications of these reforms are unknown. This study estimates the necessary reduction in adverse events to offset the costs involved (eg, non-physician providers) with adapting to these work-hour restrictions. Investigators concluded that a modest decline in preventable adverse event rates associated with discharge may be cost neutral to society. However, a much larger decline would be necessary for similar cost neutrality on teaching hospitals.