Orf is a sheep disease, due to a parapox virus. Men in close contact with these animals may be contaminated. This generally occurs during professional activities. In our clinic, located in the heart of Brussels, we were surprised by the number of orf cases encountered each year, grouped during a short three-week period. We decided to set up a prospective study of three years. Forty-four cases (14 to 64 years of age) were observed: 14 in 1998, 18 in 1999 and 12 in 2000. There were 29 men and 15 women. Only one patient had professional contact with sheep; 42 were muslims. Forty-two lesions out of 44 developed in the same time span, 10 days earlier each year. Complications observed were: erythema multiforme (7 cases), lymphangitis (3 cases), axillary adenitis (3 cases), eyelid edema (2 cases), generalized maculopapular eruption (2 cases) and contact dermatitis to the cream applied (1 case). This peculiar epidemiology can easily be explained: patients are contaminated during a religious feast, Aid el Kebir (the Feast of Sacrifice). On this occasion, they slaughter sheep, which they manipulate with bare hands. Small trauma often occur at that time. We conclude that orf is not only a professional disease but particuliar habits may cause epidemic-type contamination.