This paper relates to a special case of science-society mediation set up during the Science et Cité festival 2005. This national event took place in about twenty cities in Switzerland to promote a closer cooperation between science and society via art (theatre, music, dance, exhibitions, cinema, etc.), in order to reach the population at large. Results on the profile of the public, the role played by the cultural institutions involved, the motives of the visitors and the role of art in the science-society dialogue show that the goals aimed at by the festival's organisers were only partially reached. Moreover, the analyses shed light on the complex relation between art, science and society in public understanding of science activities.