Objectives. To determine the incidence and spectrum of significant alternative or additional diagnoses established or suggested on unenhanced helical computed tomography (CT) in a large series of patients with suspected renal colic.

Methods. One thousand consecutive unenhanced helical CT examinations were performed for suspected renal colic. All official CT reports were retrospectively reviewed, which was followed by review of all available relevant follow-up radiology reports. A selected image and chart review was also performed.

Results. Ureteral calculi were identified on 557 examinations, findings consistent with a recently passed stone were discovered on 67 examinations, and 275 CT examinations were unremarkable. An alternative or additional diagnosis was established or suggested on 101 examinations, including in 26 patients with concurrent ureteral calculi. There were 62 genitourinary and 39 nongenitourinary tract diagnoses. Eighty-seven of the diagnoses could be confirmed on retrospective image review combined with patient follow-up. There were two false-positive diagnoses for significant, alternative pathologic findings.

Conclusions. A wide spectrum of significant, alternative, and additional genitourinary and nongenitourinary diagnoses can be reliably established or suggested on unenhanced helical CT performed for suspected renal colic. These abnormalities were identified in 10% of cases in this series of 1000 consecutive CT examinations.