Technical demands, economic considerations and allocation of services around the clock bring about, that night work constantly represents a portion of 12-15% in Germany. Work against the biologic clock increases the risks for accidents and may produce health risks as sleeping or gastro-intestinal disorders, depression, cardio-vascular diseases, overweight, and a disturbed sexual activity and fertility. Adaptation to an altered day/night rhythm during night shift work takes more than a week, and even then the time shift is rarely complete. In contrast the duration of time shift is much shorter during a jetlag and is mostly completed after 2-3 days. Therefore, much less health risk is to be expected from jetlag as compared to night shift work. About 15% of all healthy adults are insufficiently adaptable to night shift work. These individuals carry a particularly high health risk, if regularly participating in night shift work.