Alveolar echinococcosis, a parasitic disease due to the larval stage of the cestode Echinococcus multilocularis, is initially located in the liver in 97% of cases. Progression is very slow and the disease remains silent for many years. The developing larva behaves like a slow-growing liver tumor that gradually invades the liver parenchyma, vessels and bile ducts. Marked granulomatosis around the larva, and the subsequent strong reactive fibrosis, contribute to the severity of the disease. Gradual extension to adjacent organs and distant metastases due to haematogenous spread can also occur. Purely extrahepatic alveolar echinococcosis is rare, but physicians in endemic areas should be aware of this possibility. Diagnostic methods have dramatically improved over the past twenty years. The clinical presentation used to be similar to that of liver cancer, with slowly progressivejaundice (due to involvement of the hilum), huge, hard and irregular hepatomegaly, and a chronic Budd-Chiari syndrome due to hepatic vein involvement. Currently, with extensive use of abdominal ultrasonography, alveolar echinococcosis is commonly diagnosed when still asymptomatic. Alveolar echinococcosis may also be revealed by a complication, such as cholangitis due to communication between the parasite mass and the lumen of a bile duct or to pigment stones accumulating above a parasitic biliary stenosis; liver abscess related to centro-parasitic necrosis; or hematemesis due to esophagal varices in case of portal vein involvement. Metastases, especially in the lungs, reveal the disease in 5% of cases.