Fifteen cohorts of healthy bathers were recruited at four Lake Leman beaches between 3 July and 23 August 1996 to assess the public health importance of cercarial dermatitis in Geneva, Switzerland. Telephone follow-up interviews were carried out after 2-7 days. Overall, 153 bathers out of 555 reported probable cercarial dermatitis at follow-up. Median daily attack rate was 27.7% (2.2-57.7%). Of the cases, 11.1% noticed more than 30 skin lesions, 19.6% described severe itching, 50.3% used a drug treatment, 3.9% visited a doctor and 15% claimed they would reduce their bathing activities. History of cercarial dermatitis, time spent in the water, hour of the day, barometric pressure and maximum daily atmospheric temperature predicted disease occurrence in multivariate analysis. While a benign disease, cercarial dermatitis may have a negative impact on the local water recreation industry. The identification of risk factors for the disease may help produce better preventive recommendations for the bathers.