Hydatid cyst, the larval cestod of Echinococcus granulosus infects both man and animal. In the last five years, fourteen cases have been surgically treated in the Universities Hospitals of Cairo (9) and Ain Shams (5). The highly infected site was the liver and the least was the spleen. On the other hand, a total of 2,871,510 sheep slaughtered in the governmental abattoirs over five years (1995-1999) showed an overall hydatidosis of 0.33%. The highly infected site was the lung followed by the liver. Cystic infection in other sites rarely occurred. Generally speaking, hydatidosis is not a so dangerous public health problem in Egypt. However, sheep play the important role in dissemination of the disease. This is due to the fact that their cysts are the highly fertile ones as compared to other animal intermediate hosts. So, the risk cycle in hydatidosis is sheep-dog-man.