Abdominal ultrasonography was performed on eight children and four adults with acute schistosomiasis mansoni, 12 chronically infected patients, and 12 noninfected individuals from the endemic area, who were paired by age and sex with the acute group. In all acute patients, lymphadenomegaly as well as liver and spleen enlargement were detected. Lymph nodes surrounding the portal vein and the hepatic artery in the hepatic hilus were visualized. In the children, the right lobe of the liver was statistically significantly larger in the acute group than in the noninfected group. The portal and splenic vein diameters were significantly larger in children with acute schistosomiasis than in the chronically infected and negative control groups. The left hepatic lobe and a longitudinal scan of the spleen in acute adult patients were statistically significantly larger than in the chronically infected and negative control groups. Ultrasonography is shown to be a useful tool for the differential diagnosis of acute schistosomiasis mansoni.