The intravenous urogram has long been the primary imaging modality in assessing acute renal obstruction. Newer ultrasound (US) techniques including pulsed and color Doppler allow the physiology of the urinary system to be interrogated via the resistive indices and ureteral jets. We sought to determine whether these new techniques would improve the ability of ultrasound to assess the presence of renal obstruction and replace the intravenous urogram in assessing acute ureteral obstruction.