Cercarial dermatitis is a parasitic impasse that has worldwide distribution. The condition manifests itself as a highly pruriginous skin rash and is due to penetration of the dermis by larval stages (furcocercariae) of avian trematodes. Many species may be responsible for this disease. In Europe the genus Trichobilharzia is widely represented, in particular by the species T. ocellata; the definitive host is the duck (Anas platyrhinchos); the intermediate hosts are snails of the genus Lymnea (L. ovata or L. stagnalis). In France, cases of cercarial dermatitis were reported in June and July 1994 to the health authorities of three départements in the Pays de la Loire Region (western France). The epidemiological situation, common to the three maintained ponds that were concerned, is as follows: high level of eutrophication of the sites, colonization of the ponds by L. ovata, and settlement by many duck colonies. The simultaneous occurrence of these three phenomena, combined with long hours of sunshine in the summer, is responsible for most of the foci of cercarial dermatitis recently described in Europe. Control of this condition is difficult, requiring strict maintenance of bodies of water and if necessary the use of molluscicides such as niclosamide. The use of praziquantel in baits for treating the definitive hosts appears to interrupt the natural cycle of the avian Schistosomatidae. In the light of the observations reported here and the analysis of recent publications, cercarial dermatitis may be regarded as an emerging disease. Its public health impact needs to be evaluated at the global level.