The objective of this study was to determine whether patients discharged from the Emergency Department (ED) with a proven diagnosis of renal colic require less total evaluation and treatment time if unenhanced helical computed tomography (CT) rather than intravenous urography (IVU) was the diagnostic imaging study used. A retrospective review was undertaken of the medical records of 98 consecutive patients with a final diagnosis of urolithiasis or renal colic evaluated with an unenhanced helical CT scan or an IVU between January 1, 1999, and December 31, 1999. All patients were managed by Emergency Physicians and discharged from the ED. The time the patient was brought to the treatment area, the time the imaging study was ordered, and the time the patient was discharged were recorded. There were 75 patients evaluated with CT scan and 23 patients with an IVU. Patients who underwent unenhanced helical CT scan were in the ED for a mean time of 291 min [95% confidence interval (CI) 266-316] and those who had an IVU were in the ED for an average of 410 min (95% CI 340-481). Use of unenhanced helical CT scan was associated with less total time in the ED compared to IVU for patients with renal colic by a significant mean of 119 min. It is concluded that ED evaluation and treatment time of patients ultimately discharged with a proven diagnosis of renal colic is significantly less when evaluated with unenhanced helical CT scan compared to IVU.