Since the start in 1988 of the present epidemic of kala-azar (visceral leishmaniasis) in western Upper Nile state in southern Sudan, the epidemiology of the disease in all parts of the Sudan where kala-azar has been reported was reassessed by the Leishmaniasis Research Group in Khartoum. In this paper, the spread of the epidemic is described among a nomadic tribe originating from southern Kordofan state, who migrate every year with their cattle to the Bentiu area in western Upper Nile state where the epidemic is still raging. 200 cases from this tribe were seen in Khartoum; another 56 cases were found during a field trip to the area. In addition, the Bentiu area was visited, where 301 cases were under treatment and another 52 of 1120 individuals screened were confirmed parasitologically. 20 cases of post-kala-azar dermal leishmaniasis were found. Parasites isolated from the nomadic tribe were of the same zymodeme as parasites isolated previously from the Nuer in western Upper Nile. The epidemiological findings in each state are discussed in relation to the tribes that were affected and the ecology of the area.