Duplex ultrasonography plays an important role in the preoperative and postoperative assessment of liver transplant patients. Before surgical intervention, the principal use of sonography is to assess the patency of the extrahepatic portal vein because a narrowed or thrombosed portal vein may preclude transplantation. Postoperatively, several potential complications can lead to allograft dysfunction (rejection, infection, vascular thromboses, and biliary tract complications). Because these complications often manifest with variable and nonspecific symptoms, diagnosing them can be difficult. Sonography is a valuable noninvasive means of evaluating postoperative complications in liver transplant patients. When vascular complications are suspected, duplex sonography is the optimal screening procedure for assessment of the vascular anastomoses. Focal parenchymal abnormalities (hematomas, infarcts, and bilomas) and localized collections of abdominal fluid are readily detected by ultrasonography and can be safely aspirated and, when infected, percutaneously drained under sonographic guidance. Sonography is less useful in the detection of biliary tract complications early after transplantation.