This is a report on 121 cases of hydatid disease of liver. The alteration of the false cyst, explaining the most common complications of the disease, is discussed. Complications were present in 61 (50.41%) of our 121 patients: calcification in 13.22%, infection in 10.74%, perforation in bile ducts in 9.91%, thorax in 5.78% and abdominal cavity in 10.74% of our cases. Diagnostic importances of clinical findings, immunoelectrophoretic studies and radioisotopic liverscanning is emphasized. In 28 cases the complete excision of cysts were carried out, in 110 cases only removal of the hydatid membrane was performed. Other therapeutic methods are discussed. Of 108 treated patients 7 died postoperatively: they were all over 70 years old.