Following liver transplantation, various complications can occur, which we then divide into those of early and late onset. These include vascular and biliary complications, fluid collections and neoplastic changes (hepatocellular carcinoma, metastases). Ultrasound is the most widespread, most accessible and the cheapest examination used for imaging liver pathology. With it, very quick and efficient diagnostics can be done right next to the patient's bed, without moving the patient elsewhere. The advantage that ultrasound and magnetic resonance (MR) have over computed tomography (CT) is the lack of ionizing radiation, which is of great importance given that the health of the patient always comes first. The most common types of ultrasounds we use while diagnosing liver pathology are color, power and pulse wave Doppler. They are used to obtain data of the blood flow in the vessels, both visually and computationally while using the resistance index, which is important when we are suspecting obstruction or stenosis of the liver blood vessels. Also, the patency of the portal vein before transplantation and the evaluation of the hepatic artery thrombosis after transplantation are performed by ultrasound. By using ultrasound contrasts, such as those filled with air or low-soluble gases, we can better describe the appearance of the liver vessels and more easily distinguish benign from malignant tumours. For better imaging of vascular structures, we can also use CT. MR, in the form of magnetic cholangiopancreatography, is more commonly used in diagnosing biliary complications and to display the biliary tree. This thesis describes the methods of detection and diagnosis of posttransplant complications and pathological changes of the liver in patients that underwent liver transplantation.