Twenty-seven cases of proven liver hydatid cysts were examined by MR and CT. On MR the cyst wall showed a rim of low signal intensity on both T2- and T1-weighted imaging. This capsule was more easily identified by MR than by CT. Specific signs of daughter hydatid cysts and detachment of the membrane were also evident by CT and MR examinations. Magnetic resonance was more effective than CT in detecting complications of the cyst; the first echo of T2-weighted imaging showed a very high signal of the hydatid content in cysts that communicated with the biliary tree or in superinfected cysts. However, MR did not help characterize solid or pseudotumoral forms of hydatid disease.