Sonograms of 35 patients with cadaveric renal allografts were reviewed. The patients included five with successful renal transplantations, seven with acute tubular necrosis, 19 with acute rejection, one with complete occlusion of the renal artery, and three with stenosis of a renal artery. During the course of acute tubular necrosis, the renal anatomy remained sonographically unaltered. During the course of acute rejection, there was a spectrum of sonographic findings including increase in renal volume, decreased amplitude of the renal sinus echoes, enlarged medullary pyramids, indistinct corticomedullary boundary, increased echogenicity of the renal cortex, areas of decreased parenchymal echogenicity, sparse cortical echoes, and perirenal fluid collections as a result of hematoma or crescentic collection of fluid around the kidney. In both arterial occlusion and stenosis, no sonographic abnormalities of renal anatomy were seen and the only finding was lack of normal post-transplantation hypertrophy. Our study encourages the use of sonography in acute post-transplantation renal failure. If serial ultrasound studies are available and correlation with clinical and laboratory data and nuclear medicine studies are obtained, the correct diagnosis may be reached without the use of invasive procedures.