Background: The aim of the study was to describe the diagnostic efficiency of computer tomography in the differentiation of urgent complications after renal transplants. The most common situation which needs to be explained using imaging diagnostics is acute abdominal pain in patients with renal grafts shortly after the operation (within a few weeks) in conditions of emergency. Most of the examinations were performed without contrast enhancement to avoid possible nephrotoxicity of the contrast media following the transplantology rule. The difference in the efficiency of the two methods with or without i.v. infusion contrast is emphasized. Material/Methods: Thirty-two CT's of 22 patients with complications after renal transplants were analyzed by comparing their clinical data. The images were compared with regard to size, parenchymal density, and homogeneity of the renal graft. Furthermore, contrast enhancement homogeneity with preservation of the cortical-medullar differentiation, width of the excretory system and the ureter, and presence of circumgraft fluid collection with a designation of its density and probabiliter specify (lymphocele, abscess, or hematoma) were also considered. When possible, the lumen of the renal vessels and the state of vessel anastomosis were recorded (CT angiography and some good-quality contrast examination). Also, other pathologies in the examined region were considered as a potential cause of the acute pain (e.g. multiplanar reconstruction was performed to obtain proper images of the lumbal spine). Results: CT of the abdomen explained clinical problems in 21 of the 22 patients (95%). Most examinations showed that the fluid collections were lymphocele, mainly small and without compression of adjoining structures, which are considered normal after transplants. Large fluid collections requiring decompression were found in 6 patients (including 2 hematoma and 1 with abscess). Causes unrelated to renal graft were found in 4 cases. Conclusions: Computer tomography, although it is not included in post-transplant monitoring procedures, appears to be a very useful method to enhance ultrasound imaging in cases of complication after renal transplant in a situation where MRI is not available. Its efficiency is increased to a great degree using contrast enhancement, which allows evaluation of excretory system morphology, the widths of walls, and the lumen of the ureter and renal vessels and, more specifically, to evaluate renal parenchyma.