The purpose of our study was to determine the value of unenhanced CT in the diagnosis of acute flank pain. We determined the accuracy of unenhanced Ct for stone detection as well as the detection of abnormalities unrelated to stone disease.During an 18-month interval, 292 patients with acute flank pain were imaged with unenhanced CT. Confirmation of the CT diagnosis was obtained for 210 patients: One hundred patients were proved to have ureteral stones based on other imaging studies (58 patients), lithotripsy (seven patients), ureteroscopic stone extraction (five patients), and stone recovery (30 patients). One hundred ten patients were proved not to have ureteral stones based on other imaging studies (24 patients), failure to recover a stone (56 patients), or a confirmed diagnosis unrelated to stone disease (30 patients). This latter group of 30 patients included diagnoses of adnexal masses (eight patients), appendicitis (five patients), diverticulitis (four patients), and common bile duct stones (three ...