Precautionary Principle (PP) and its application to environmental and health policy appear in the 70's and from that time is introduced more and more frequently in different international treaties and conferences on environment and health. PP is a risk management policy applied to scientifically uncertain circumstances where it is necessary to act against a potentially harmful risk factor without waiting for more accurate information. When this situation takes place at the workplace, the risk management is an Employer's task. The employer can use different instruments, including the occupational physician's advise, to reach their target. After identification of possible health and safety risk factors and after characterisation of a non-admissible risk for worker's health, the Employer must chose which precautionary actions to take, also in function of economic, technical and judicial needs and restrictions. This action can be the application of measures of "prudent avoidance" through steps such as health surveillance, until more radical measures are taken by using P.P. The Occupational health specialist that is already operating of the work place with characterised and well known risk factors should introduce the instruments, in the health surveillance activities, that may detect possibly adverse effects related to risk factors characterised by scientific uncertainty. This is very important whenever the employers don't have the possibilities or are not sensitive enough to take other kinds of precautionary measures. Moreover, the occupational physician should play an active role also in the risk assessment phase by defining those chemicals or physical agents still characterized by scientific uncertainty.