Hydatid liver cysts are caused by infection from tapeworm Echinococcus granulosus or, less commonly, Echinococcus multilocularis. These cysts are most commonly found in the right lobe of the liver. Small cysts are usually asymptomatic but larger cysts may cause pain in the right upper abdominal quadrant. They may rupture into the peritoneal cavity, causing fatal anaphylactic shock. Treatment includes surgical resection. Mebendazole should be started after surgery.