A total of 24 cases of hepatic alveolar echinococcosis (HAE) due to Echinococcus multilocularis was assessed by US and CT. The diagnosis was confirmed in all cases by immunologic and histologic study. Both US and CT patterns of HAE showed changes of liver morphology in both contour and size. Abnormal areas of parenchyma were nodular or in fields, irregular, heterogeneous, and basically echogenic. On CT these lesions were hypodense (30 to 40 HU) and did not show enhancement after administration of intravenous contrast medium. Clustered microcalcifications were encountered within the abnormal parenchymal fields in 50% of cases, and necrotized zones occurred in 40% of cases. Dilatation of intrahepatic bile ducts was commonly seen, especially on US; hilar involvement was frequent. Follow-up by both techniques can display increases of primary lesions, occurrence of new foci, and local or regional extensions. Precise evaluation of the lesions arising from correlative use of US and CT permits adequate therapeutic management.