The value of unenhanced spiral CT (UESCT) for investigating acute flank pain suggestive of urinary tract calculi is increasingly appreciated in the last few years. Recent studies have identified the advantages of UESCT in recognizing alternative findings within or outside the urinary tract. We sought to determine how narrowing the referral base for the UESCT would affect the discovery of potentially significant alternative findings in patients with acute flank pain suggestive of renal colic. Between January 1999 and December 1999, 425 patients, 271 (63.8%) men and 154 (36.2%) women who were 1-90 years old (mean 45.7 years old) with acute flank pain were studied with UESCT. CT studies were solely ordered by urologists, and only patients with intractable renal colic or patients that returned more than once to the emergency room with the complaint of acute flank pain were studied. A calculus within the ureter was diagnostic of an obstructive stone. Any other abnormality within the abdomen and pelvis was reported. A ureteral calculus was detected on 251 (59%) CT scans. Nineteen (4.5%) CT scans were consistent with recent excretion of a stone. In 112 (26.3%) CT scans, the cause for the patient's acute flank pain could not be explained. Forty-three (10.1%) alternative significant diagnoses that explain the patient's complaints were found. Nineteen (44%) were findings related to the urinary tract, and 24 (56%) were not related to the urinary tract. Ninety-seven (22.3%) additional findings not significant to the patient's current complaint were also reported. Even when narrowing the indications for the UESCT, about 10% of significant alternative findings to urinary stones were encountered. The variety of diagnoses found unexpectedly on the UESCT that alter a patient's management demonstrates the pivotal role of UESCT in triaging these patients rapidly towards optimal therapy. The UESCT can be used as a useful screening tool, sometimes revealing the exact pathology and sometimes directing the radiologist to the modality by which to continue.