Background: Patients with renal colic commonly present to the emergency department (ED) and are usually treated with analgesics, antiemetics, and hydration. A common approach in evaluating patients with suspected renal colic is to use computed tomography (CT) scan which carries a heavy burden of both radiation exposure and expense. Objectives: We compared diagnosis and treatment plans before and after CT in patients with suspected renal colic. Our aim was to evaluate how often changes in diagnosis, treatment, and disposition are made after obtaining CT scans. Methods: In this prospective observational study, we enrolled a convenience sample of ED patients with suspected renal colic for whom CT was planned. Inclusion criteria were: chief complaint consistent with renal colic, most likely diagnosis is renal colic, age 18 to 50 years, and clinically stable. Primary exclusion criteria were: chronic kidney disease (Cr >2.0), urinary tract infection, recent CT (<6 months), and history of previous kidney stone. Pre-CT and Post-CT surveys were completed by the treating provider. Results: Ninety-three patients were enrolled. The discharge diagnosis was renal colic in 62 patients (67%). CT confirmed obstructing kidney stone or bladder stone in 50 patients (median size 2.5 mm) with associated hydronephrosis in 49 patients. UA showed blood in 46 (92%) of these patients. Of the 42 patients with no obstructing stones, renal colic was diagnosed in 12. Alternative diagnoses were most commonly musculoskeletal pain (11) and non-specific pain (13). There were 2 cases of important alternative diagnoses provided by CT - one ovarian tumor and one diverticulitis. After CT scan, urology was consulted for 13 patients and 7 patients had changes in disposition (all admitted). Fifteen patients were prescribed alpha-blocking medicine after confirmation of obstructing kidney stone. Sixteen providers felt that CT would not change management. In these cases, CT offered no alternative diagnosis and didn’t change disposition. Seventy-seven providers thought the CT would possibly or definitely be useful. All cases of important alternative diagnoses and disposition changes were among these. Conclusion: CT scan commonly refutes provider suspicion of renal colic. At the same time, it provides important alternative diagnoses and can often alter management and disposition. Providers who felt that CT would not change management were always correct.