Stakeholders' participation is increasingly considered as a plain part of the assessment and the management of a contaminated site. It is also acknowledged to be a difficult and sometimes risky challenge. Beside virtual experiments on "test groups", there is very little feedback on real cases of extensive stakeholders' participation on contaminated sites in Europe. No guideline or support document exist in Europe to help to organize Stakeholders' participation. We present here the real case of a Southern area of the town of Vincennes near Paris: following a high number of cancers among children in a school in the vicinity of a former industrial site and a hospital incinerator, the Health Ministry set up an independent Scientific Committee in charge of designing the epidemiological and risk assessment studies, of reviewing theirs results and of issuing recommendations. The Prefect directed a Participation Committee gathering all stakeholders in the aim of sharing all information available on the site, of discussing the results of the studies and the conclusions of the Scientific Committee and collecting opinions and expectations of each stakeholder in order to prepare decisions. Numerous studies were conducted. The Scientific Committee reviewed more than 30 protocols and reports. This experience is discussed here with regard to major questions on stakeholders' participation in site assessment and management, such as the communication between experts and non-experts and between experts of different fields (health scientists vs. environmental engineers), the impact of the media, the psychological impacts, the "crisis vs. non-crisis" aspects of participation. The discussion integrates other experience gathered on stakeholders' involvement It leads to the identification of some ingredients for an efficient stakeholders' participation, event if the specificity of each case, and the importance of spontaneity, reactivity, is recognized.