We read with interest the article by Jagsi et al,1 who reported that a considerable amount (24%) of adverse events were attributed to mistakes, and the most common reason for mistakes was excessive work hours. Working 80 to 100 hours weekly is dangerous for interns and patients, and in these last years, US residents were restricted to work less than an average of 80 hours per week and no more than 30 hours of continuous duty. According to the extension of the European Working Time Directive to cover physicians in training, 58 hours per week are allowed for resident physicians, falling to 48 by 2009. Shift work is associated with increased mortality,2 and the relative risk of incidents increases over successive night shifts, being 6%, 17%, and 36% higher on the second, third, and fourth night, respectively.3 In addition to excessive charge of work hours, getting adequate sleep is the crucial point. Mental performance respects a circadian rhythm, with a peak that tends to fall with increasing sleep loss.4 A complete loss of sleep for 2 or 3 consecutive nights exposes one to temporary visual hallucinations, bizarre behavior, and psychoticlike symptoms.4 Safety is a primary concern, especially in health care settings, and sleep deprivation can impair medical procedure–related performance.5 However, the total rough number of hours of sleep is not a reliable measure. A complete sleep cycle lasts 90 minutes, and during prolonged continuous work shifts, residents should be allowed to take at least 2 consecutive sleep cycles to get restored and reduce harmful consequences.