Renal US is one of several imaging modalities available to the EP in the evaluation of patients with acute urologic disorders. It offers excellent anatomic detail without exposure to radiation or contrast agents but is limited in its assessment of renal function. It is an important alternative to helical CT scanning for evaluating renal colic, especially in children and pregnant women. It has an important role in excluding bilateral renal obstruction as the cause of acute renal failure. It is likely that Doppler renal US also will take on a prominent role in the evaluation of renal vascular disorders. It already has become the standard of care in the management of renal transplant patients. Bedside emergency renal US performed and interpreted by EPs with limited training and experience is increasing in use and gaining acceptance. At present, the primary role of renal US is to identify hydronephrosis in patients with renal colic or acute renal failure but, in the future, its role likely will expand as technology advances and its use increases. In many patients, bedside renal US may obviate the need for further diagnostic workup and speed the diagnosis and treatment of an emergency patient.