The first mention in Africa of ocular lesions and of blindness due to onchocerciasis was made by Hissette in Zaïre in 1931, although the disease had already been known there since 1903. On a map of Zaïre were indicated all the known data of the geographical distribution of onchocerciasis: data from the literature, from field work and from the patients seen in Kinshasa. An estimation of the relative incidence of the disease was made by comparing the number of patients with the number of the latest population census for each administrative zone. The environmental and developmental factors determining the epidemiological aspects are discussed. The clinical aspects of the typical eye symptoms are reviewed. Their correlation with age, with immunology and with some specialized eye examinations are discussed.