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Human onchocerciasis is found along the Nile in Northern Sudan, on the border with Ethiopia and in the Southern and Western Sudan--all areas where there is fast flowing water suitable for S. damnosum S.L. (in Sudan, the only fly in which the O. volvulus has been found) to breed. Epidemiological studies of this disease are still in progress however it is clear that in the huge area between Bahr El-Arabe and the white Nile, which is the most serious focus with blindness rates equalling or exceeding those in the worst affected foci elsewhere in Africa. Infection rates and parasite populations are highest in villages situated on rivers--near the probable breeding sites. Intensity of infection is generally highest in skin snip taken from the pelvi region, where the palpable nodules are more frequent. Microfilariae are commonly detected in the anterior chamber of the eye and in the peripheral blood. Fundus oculi lesions have been also detected in significant numbers causing impairment of vision and blindness, specially in the group of old people. Males are more commonly infected than females. These data provide a reasonable, though far from complete, account of the present situation concerning the importance and severity of onchocerciasis in this part of Sudan.