A prospective study during 28 months at the Regional Hospital Center of Bouake (Ivory Coast) allows to gather 124 cases of Buruli ulcer. Today, this atypical cutaneous mycobacteriosis is in full expansion in West Africa. The pathogen agent, Mycobacterium ulcerans, causes, by its toxin, a subcutaneous necrosis often extended, followed by an ulceration which clinical characteristics are sufficient for the diagnostic. The endemic progression reason may not be caused by the modification of patients receptivity, but rather by the natural environment modification. In particular, the improving number of some soft water fish (Tilapia) which could have a germ tank.