This paper describes an outbreak of dracunculiasis in Mazmum, a town in central Sudan. The study included collection of clinical and epidemiological data from 319 patients treated in hospital, a review of the hospital records, a house survey covering a sample of 757 subjects, a school survey covering 1390 schoolchildren, and examination of water sources. The overall incidence of the disease was 23.4%, with most cases appearing in the agricultural season (July-October). Incidence was highest in young females but most severe disability occurred in male patients aged > or = 20 years, of whom more than 60% were unable to work for more than 4 weeks. The disease is transmitted in shallow natural pools, artificial ponds and trenches in rocky hills that hold rain water. All these sources were found to be infested with Cyclops. The outbreak is attributed to deterioration in the structure and management of the water sources, together with a massive population influx from other endemic areas. These observations underscore the importance of co-ordinating efforts to eradicate the disease from African countries.