In modern society, more and more people work during 'non-standard' working hours, including shift and night work, which are recognized risk factors for health, safety and social well-being. Suitable preventive and protective measures are required to mitigate the adverse effects and ensure that the worker can cope satisfactorily. These are based mainly on the organization of shift schedules according to ergonomic criteria and on specific medical surveillance. Occupational medicine has to consider very carefully the several factors (psycho-physiological, pathological and social) that can influence tolerance and/or maladaptation.