Grey scale ultrasound provides a valuable non-invasive method of investigating the kidneys. It is usually a complementary examination to intravenous urography. When the ultrasonic findings are considered along with the clinical history, the results of the urogram and the results of any other relevant investigations then an accurate diagnosis can often be made. Ultrasound is of particular value in the investigation of renal masses, the non-functioning kidney, perinephric fluid collections, patients in renal failure and in the post-operative assessment of renal transplant patients.