Obstruction of a major hepatic vein, or major portal vein, or biliary tree branch causes atrophy of the related hepatic region, and frequently, hypertrophy in the remaining liver-the atrophy-hypertrophy complex (AHC). Whether hydatid cysts can cause AHC is controversial. The records of 370 patients who underwent surgery for hepatic hydatid disease between August 1993 and July 2002 were evaluated retrospectively. Excluding six patients with previous interventions on the liver, AHC had been recorded in the operative notes of 16 patients (4.4%); for all patients, a cyst located in the right hemiliver had caused atrophy of the right hemiliver and compensatory hypertrophy of the left hemiliver. The computed tomography images of seven patients were suitable for volumetric analysis. The median (range) right and left hemiliver volumes were 334 (0-686) ml and 1084 (663-1339) ml, respectively. The median (range) cyst volume was 392 (70-1363) ml. AHC due to Echinococcus granulosus was confirmed by objective volumetric analysis. The presence of AHC should alert the surgeon to two implications. First, pericystectomy may be hazardous due to association with major vascular and biliary structures. Second, in patients with AHC, the hepatoduodenal ligament rotates around its axis; this should be considered to avoid vascular injury if a common bile duct exploration is to be performed.