Computed tomography (CT) is the diagnostic standard in Emergency Department evaluation of suspected renal colic but delivers substantial radiation. We determined the frequency of CT scan in suspected renal colic, diagnosis and outcome, and cumulative CT scans per patient. A retrospective chart review with waiver of informed consent was conducted. A total of 356 patient encounters were reviewed from January to October 2003. Mean age was 39 years. Seventy-four percent included a CT scan, with 38% normal, 58% showing urolithiasis, and 1% showing emergent etiologies. Six percent of patients undergoing CT were admitted for urolithiasis, and 6% had a urologic procedure within 7 days. Sixteen percent of patients did not have a CT scan, and 79% underwent two or more CT scans. Emergency Department patients presenting with symptoms suggesting renal colic are likely to undergo CT on multiple occasions. Radiation exposures from repeated CT scans are substantial, and a clinical decision rule for this scenario is needed.