Postoperative complications after renal transplantation, such as hematomas, abscesses, urinomas, lymphoceles and obstruction of the ureter, can be diagnosed by means of sonography. Early vascular complications, such as venous thrombosis and arterial occlusion or stenosis, can be recognized by duplex sonography and accurately depicted by angiography to allow planning of surgical intervention. Stenosis of the renal artery is amenable to treatment by percutaneous angioplasty. Parenchymatous complications (acute tubular necrosis, acute rejection, cyclosporin-A-toxicity) can cause changes in the intrarenal flow patterns at duplex sonography, but this examination does not allow accurate diagnosis and differentiation of these changes. Magnetic resonance imaging is a very promising method for the differential diagnosis of parenchymatous complications.