Single or multiple hydatid cysts of the liver are frequently observed in Italy and the Mediterranean countries. They are swellings caused by the hexacanth larva of a small cestode, Echinococcus granulosus. This must be distinguished from E. multilocularis, which is responsible for alveolar cyst, and is common in central-eastern Europe, but rare in Italy. An account is given of the development cycle of the intermediate and final host, the protean symptomatology (dependent on the siting of the cyst in the liver and the presence of complications), and the radiological, ultrasound, biological and anatomical diagnosis of this form. Diagnosis is much dependent on the examinations of first choice (currently echotomography, plus immunoelectrophoresis and immunofluorescence that permit epidemiological control of the community and serological follow-up after surgery). Computed tomography is of assistance in the approximately 25% of cases in which echotomography is not conclusive, while angiography is called upon to provide very precise mapping of the supramesocolic region. Surgery requires two fundamental stages: sterilisation of the parasite and treatment of the pericystium. It involves external or internal shunting, or partial or total resection, depending on various factors, particularly the thinness or thickness of the pericystium, the absence or presence of infection, and the site, volume and number of the cysts. Medical management with mebendazole and its derivatives is still chancy, both on the strictly therapeutic plane and with regard to the prevention of secondary, spontaneous or postoperative dissemination.