Mbam, a focus of onchocerciasis outbreaks, is located in the forest/savannah transition zone of Cameroon. Transmission of the disease in this area is similar to that sometimes observed in West Africa. Geographical factors affecting transmission must be identified to determine the areas for priority action. The locations of breeding sites for black flies (the vector of the disease) and factors favorable to their dispersion, the social behavior of these population and the way that she occupy space, must be investigated to identify areas in which the flies and man are in close contact. This geographical study shows that the closest contact between men and black flies occurs in cocoa plantations, due to the proximity of the breeding sites. The areas of closet contact for women and children are unknown, but their identification is important because women and children may be bitten by the flies during their daily activities.