To compare non-contrast-enhanced computed tomography (CT) and intravenous urography (IVU) in the evaluation of patients who present with acute flank pain and in whom ureteric obstruction is suspected. The findings at non-contrast-enhanced CT and IVU in 20 patients with acute flank pain were compared for the presence or absence of ureteric obstruction and delineation of ureteric stones. Twelve of the 20 patients had non-contrast-enhanced CT and IVU findings consistent with ureteric obstruction. Of these 12 patients, five had a ureteric stone that was demonstrated on both non-contrast-enhanced CT scans and IVU radiographs, six had a stone that was depicted on non-contrast-enhanced CT scans only, and in one patient a stone could not be delineated definitively on either non-contrast-enhanced CT scans or IVU radiographs. Eight patients had findings at non-contrast-enhanced CT and IVU consistent with the absence of obstruction. Non-contrast-enhanced CT is more effective than IVU in precisely identifying ureteric stones and is equally effective as IVU in the determination of the presence or absence of ureteric obstruction.