A POTENTIAL PUBLIC HEALTH PROBLEM: Cercarial dermatitis is caused by the infestation of the skin by cercariae of nonhuman schistosomes whose commonest hosts are aquatic birds. Human contamination can occur during swimming in fresh water infested with cercariae and notably ducks. Its geographic distribution is worldwide and is increasingly described in France during the summer months. FROM A CLINICAL POINT OF VIEW: A diffuse eruption composed of prurigenous maculopapules appears within the 24 hours following exposure. Regression is spontaneous within one day to three weeks. PREVENTION IS ADVISABLE: Treatment is symptomatic in the majority of patients. The optimal prevention, for bathers, is to swim in sufficiently deep water.