Hydatid cyst rupture into the biliary tree may involve the common hepatic duct, lobar biliary branches, or the small intrahepatic bile ducts. We studied seven patients with hydatid cyst rupture into the larger bile ducts in whom sonography suggested the diagnosis. The findings included an echogenic cyst in all cases; intrabiliary hydatid material (echogenic or nonechogenic daughter vesicles and/or echogenic fragmented membranes) in six patients; and cyst-bile duct communication (observed in five cases as an interruption in the cyst wall adjacent to a bile duct). In the four cases in which CT was performed, both the cyst and high-density linear intrabiliary material were seen; in three patients, cyst wall rupture was detected. Sonographic and CT demonstration of a hydatid cyst in the liver together with intrabiliary hydatid material suggests rupture of the cyst into the biliary tree. In some cases, the diagnosis is reinforced by the detection of the communication itself.