A hyperechoic renal pseudotumour caused by packing an operative renal defect with retroperitoneal fat has been previously described. The authors describe eight patients who underwent such packing of a renal defect and for whom ultrasonography was later performed to determine the frequency of pseudotumours and their ultrasonographic appearance. In four patients an obvious surgical defect but no pseudotumour was apparent in the renal parenchyma. In the others a pseudotumour had developed: in two the mass was hyperechoic, as previously reported, but in two the mass was isoechoic. The isoechoic pseudotumours were initially diagnosed as probable carcinomas by the ultrasonographer. Correlation with the surgical history and computed tomography scans led to the correct diagnosis.