With growing concern over the impact of intern sleep deprivation, this prospective study provides an error analysis comparing incidence rates during a traditional work schedule versus an intervention one. Investigators studied interns rotating though an academic intensive care setting and used a multidisciplinary approach to identify incidents, including direct observation. Results encompassed more than 2200 patient-days. The study found nearly 36% more serious medical errors and 5.6 times more serious diagnostic errors among interns working a traditional schedule (more than 24 hours in a row) than among interns working shorter shifts. The authors suggest that eliminating extended work shifts and reducing the hourly burden of an intern’s work week may reduce the incidence of serious medical errors.