Increasing variety in working patterns and the appearance of new forms of shift schedules in the different occupational sectors, including health services, have raised great concern about the quality of working life and job performance. The aim of this paper is to present a systematic review of the literature on the effects on health of irregular schedules in healthcare professionals. Computer and manual searches of databases, and discussion with experts, were used to identify relevant studies. No conclusive evidence was found to favour any particular work system, although there is evidence that extended workdays (9-12 h) should be avoided as much as possible. There is need for carefully designed studies in order to evaluate the long-term consequences of work schedules in healthcare workers.