The appropriate treatment of hydatid cysts of the liver is determined by several factors, namely the patient, the cyst, the therapeutic resources and the physician. Characteristics of cysts, can be described by ultrasonography (US). Based on US images, we can classify hydatid cysts, according the evolutionary phase of the larval parasite and to choose the most appropriate therapeutic approach. US is also important to evaluate the efficacy of the treatment. Concerning the therapeutic methods, surgery had long been the only treatment available for the hydatid cyst of the liver. Beginning the 1970s benzimidazoles, Mebendazole and Albendazole, have been used for the treatment of the hydatid disease and in the early 1980s, with the development of diagnostic US, the deliberate puncture of abdominal cysts, particularly those in the liver, was evaluated this lead to puncture/aspiration, followed by injection of a scolicide which became a therapeutic method known as puncture, aspiration, injection and re-aspiration (PAIR). So, according to the cyst's characteristics based on US evaluation we can establish a therapeutic strategy: cysts type 1 and 3 may be treated by chemotherapy. Alternative treatment should be PAIR but only if the cysts cannot be treated with benzimidazoles. If there are contraindications for PAIR and chemotherapy the treatment should be surgical. Type 2 hydatid cysts can be treated by PAIR following initial treatment with benzimidazoles. If PAIR is not feasible or there is no evidence of degenerative changes after chemotherapy, surgery is indicated. Type 4 cysts are usually inactive and, in these cases, treatment is not indicated. If there is evidence that the cysts contents are still viable PAIR may be indicate. If PAIR is not possible, surgery is the method of choice. Cysts type 5 do not require treatment.