A cross-sectional survey of schistosomiasis was carried out in five villages around the Elziedab irrigation scheme, in the north, and three villages in the Gezira-Managil area in central Sudan. Stools and urine from 53% (2832 individuals) and 72% (3684 individuals) of the population of these villages, respectively, were examined using the modified Kato thick smear for stools and sedimentation for urine. Clinical history and examination were done on 2832 subjects (53%) in Elziedab and on 893 (18%) randomly selected samples in Gezira-Managil. Prevalence of Schistosoma mansoni was 36% in Elziedab and the mean egg count was 150 eggs per gram of faeces (e.p.g.). Prevalence of bloody diarrhoea was 6%, hepatomegaly 6% and splenomegaly 10%. There was a significant association between these parameters and infection in the age group 10-24 years. Prevalence and intensity in Gezira-Managil area were significantly higher than in Elziedab, 52% and 234 e.p.g. Prevalences of bloody stool 29%, hepatomegaly 17% and splenomegaly 15% were also significantly higher than in Elziedab. These parameters were unrelated to the presence of eggs in the stool. Advanced hepatosplenic schistosomiasis is less than 1% in both areas. While S. haematobium was not found in Elziedab, its prevalence varied from 10 to 15% in Gezira-Managil area. In conclusion, S. mansoni is much less prevalent in Elziedab than Gezira, signs and symptoms are much less prominent in Elziedab, and most of the symptoms are unrelated to the presence of eggs in the stool.