PIP: An estimated 17.7 million persons, most of them in Africa, are infected with the parasite Onchocerca volvulus. Onchocerciasis has caused blindness in 270,000 and left another 500,000 with severe visual impairment. Onchocerciasis also can cause disfiguring skin changes, musculoskeletal complaints, weight loss, changes in immune function, epilepsy, and growth arrest. The development of ivermectin and its donation by the manufacturer has reduced transmission in many parts of Africa and Latin America. Progress in developing a drug that can destroy adult worms has been slow, however. The immediate need is to extend ivermectin mass distribution to as many endemic areas as possible on a continuing basis, with steps toward community ownership of such programs. This article presents a comprehensive review of the literature on the epidemiology, parasitology, vector, symptoms, diagnosis, and treatment and control of onchocerciasis. Future research aims include fuller understanding of the parasite and its relationship with the host, the nature of the systemic effects of O. volvulus infection, the natural history of skin disease, and a better appreciation of the social and economic consequences of this parasitic disease.