The present review summarizes the prevalence, clinical phenomena, and pathogenesis of sleep and wake disorders in shift workers. Insomnia and hyper-somnolence occur in more than 50% of shift workers, mainly in association with the night shift. Circadian rhythm disruption is the major determinant of these disorders. Furthermore they are frequently associated with psycho-social problems and somatic diseases. In more than 20% of the shift workers problems are so pronounced, that they fail to adapt to the rotating schedules. This is defined as ‘shift maladaptation syndrome’.