Ultrasound is an effective means of detecting renal stones in patients with hydronephrosis. The filled urinary bladder in a normal person under hydration frequently results in the sonographic appearance of minimal or moderate hydronephrosis. For optimal visualization of stones and associated acoustic shadows, six patients with radiographically opaque renal stones were evaluated with fluid-loaded renal ultrasonography, which was compared to conventional renal sonogram in basal state. Although ultrasound in basal state can be used for detection of intrarenal lithiasis, fluid-challenged renal sonogram appears more accurate for the determination of contour, location, size, and number of small stones. In one case, this fluid-loaded ultrasound well demonstrated the tramline appearance of an isolated renal artery, which mimics stone before fluid challenge.