Sonography is the best screening modality to evaluate patients presenting with renal insufficiency. Ultrasound findings can be normal in patients with renal disease, especially in prerenal azotemia and acute parenchymal renal disease. Echogenic kidneys indicate the presence of parenchymal renal disease; the kidneys may be of a normal size or enlarged. Small kidneys suggest advanced stage chronic kidney disease. Uncommonly, cystic disease of the kidney, especially adult type polycystic kidney disease may be the cause of the patient's renal insufficiency with bilaterally enlarged kidneys containing multiple cysts of various sizes. If hydronephrosis is present, the level and cause of the obstruction should be sought. When ultrasound cannot diagnose the level and cause of obstruction, other imaging modalities, including CT and MRI may be useful. When renovascular disease (arterial stenosis or venous thrombosis) is suspected, spectral and color Doppler can be useful in detecting abnormalities.