A reliable preoperative detection and characterization of all liver lesions is necessary for the clarification of the operability of a patient. In patients, who are considered as good candidates for a partial liver resection, a double spiral-CT with an oral bowel opacification and an intravenous contrast medium administration is recommended. In those patients, who continue to be candidates for partial liver resection after CT, a CT arterioportography with arterial and portalvenous liver enhancement should be performed as the present gold standard of preoperative liver diagnostics. The aim of CT arterioportography is the further selection of patients for liver surgery. Because of its high specificity, MRI is useful for the characterization of liver lesions of unknown histology. For the differentiation between malignant (metastases) and benign (hemangioma) liver lesions, MRI is the method of choice. Because of the expected technical developments of MRI, a short-term comparison of CT and MRI in prospective studies is necessary.