Hydatid cysts of the kidneys were explored by ultrasound in 43 patients between 1978 and 1982, diagnosis being confirmed by operation. Cases included 33 adults and 10 children under 15 years. Ultrasound images of renal hydatid cysts are analyzed, and correlated with the classification into 5 types proposed in the literature and based on their natural history. This non-invasive technique, when associated with intravenous urography, is of primary diagnostic importance, particularly in countries where these cysts are endemic. Ultrasound imaging assists positive diagnosis in a large number of cases, acts as a guide to complementary explorations when these are required, and enables detection of extrarenal locations of hydatidosis. Differential diagnosis of ultrasound images is discussed, and emphasis placed on the advantages of using this technique in countries where the affection is endemic, particularly its low cost.