Carefully conducted ultrasound and spiral computed tomography accurately characterize the majority of small incidentally detected renal masses. Masses greater than 2.0 cm that are solid or indeterminate should be excized. Masses less than 1.5 cm that cannot be characterized as benign should be followed up with computed tomography. Spiral unenhanced computed tomography is a promising new method for diagnosing ureteric colic. The renal parenchymal changes shown by ultrasound and computed tomography in acute infection should be described by the unifying term 'acute pyelonephritis'.