Human echinococcosis is a parasitic disease caused by tapeworms of the genus Echinococcus. The 2 most important forms of the disease in humans are cystic echinococcosis (hydatidosis) and alveolar echinococcosis. Humans are infected through ingestion of parasite eggs in contaminated food, water or soil, or through direct contact with animal hosts. Ingested eggs from animal feces (which may be present on the fur of dogs or other animals) hatch in the gut and release oncospheres (immature forms of the parasite enclosed in an embryonic envelope). Oncospheres penetrate the intestinal wall, migrate via the circulation, and lodge in the liver or lungs or, less frequently, in the brain, bone, or other organs. Alveolar echinococcosis occurs only in the northern hemisphere, in geographically limited foci (endemic areas) of west-central Europe. The presence of infected foxes in large cities of Europe and northern Japan 10% (in city centers) to 50% (in the suburbs) may be found in cities of the European endemic areas (such as Zurich or Geneva in Switzerland, Stuttgart in Germany, or Nancy in France). This and a newly recognized trend of infection in dogs and cats in endemic areas in Europe may lead to major changes in the human populations at risk in the near future. The asymptomatic incubation period of the disease can last many years until hydatid cysts grow to an extent that triggers clinical signs. Non-specific signs include anorexia, weight loss and weakness. Other signs depend on the location of the hydatid(s) and the pressure exerted on the surrounding tissues. Treatment varies depending on the type, location, and size of the cyst and on complications. Surgery, sometimes via laparoscopy, can be curative. Albendazole is often given before surgery to prevent metastatic infections that can occur if cyst contents spill during the procedure. In some centers, percutaneous aspiration under CT guidance is done, followed by instillation of a scolicidal agent and reaspiration.