Public health crises are today a major topic of concern. At the time of the public health crisis from November 2003 to February 2004 in the Pas-de-Calais Department - the first signs of the epidemic had been detected on October 23, 2003 - it appeared indispensable for the Parliamentary Office of the Evaluation of Scientific Choices and Technologies to provide Parliament and public opinion with information gained from experience about the scientific data available about legionnaires' disease and the difficulties in managing public health crises. The report of the public hearing produced by the Parliamentary Office on January 29, 2004 is a contribution that is rich in lessons for the future management of public health crises and for the implementation of effective prevention policies.