Demonstration and localisation of hydatid disease in the liver by ultrasound was successful in 41 patients (35 with cystic and 6 with alveolar disease). In cystic hydatid disease the demonstration of a cyst which contains a daughter cyst (5 of 35 cases), as well as a cystic conglomerate enclosed in a smooth capsule (17 of 35 cases), is typical for the disease. In 22 patients ultrasound alone provided the correct diagnosis. In the alveolar form the ultrasound findings were not typical for the parasite and could not be differentiated from solid or necrotising malignant tumour of the liver. The ultrasound method is thus of great value in the diagnosis of cystic hydatid disease, but if the findings are unclear--especially if the alveolar type of disease is suspected--further studies of the disease, in particular angiography, must be undertaken.