This study was conducted to assess the diagnostic yield of B-Mode Ultrasonography compared to unenhanced helical CT scan in detecting urinary stones in patients with acute renal colic. This retrospective study comprised of 156 patients who underwent unenhanced urinary tract CT scan and ultrasonography for suspicion of urolithiasis. Both techniques were used to determine the presence or absence, site, size, and number of urinary stones, as well as presence of any other intra-abdominal pathology. For statistical analysis, the sensitivity, specificity, predictive values, and diagnostic accuracy of ultrasonography were measured considering unenhanced CT scan as a gold standard. Unpaired two-tailed student's t-test was used for comparison between mean size of true positive, false positive, and false negative stones. There were 68 patients having 115 urinary stones. Ultrasound identified 54 stones, missed 43, and falsely diagnosed 18 stones. The mean size of true positive, false positive, and false negative stones were 4.8 +/- 3.3 mm, 6 +/- 1.8 mm and 4.18 +/- 3 mm, respectively. There were 23 patients with other intra-abdominal pathologies, equally detected by both techniques. Ultrasound helped in identifying the cause of acute flank pain in 62% of cases. The overall sensitivity, specificity, positive and negative predictive values, and accuracy of ultrasonography in the diagnosis of renal stone disease were 58%, 91%, 79%, 78%, and 78%, respectively. Our study suggests that, despite its limited value in detecting urinary stones, ultrasonography should be performed as an initial assessment in patients with acute flank pain. Unenhanced helical CT should be reserved for patients in whom ultrasonography is inconclusive.