We read the interesting article by Greenwell et al. about their experience with unenhanced spiral CT for the assessment of acute loin pain suggesting renal colic. We would like to question the accuracy of stating a sensitivity of 98%. From our understanding, a test with high sensitivity such as that quoted produces a few false-negative results, i.e. accurately identifies those who do not have the variable being investigated. Patients with negative CT findings and no subsequent stone passage were deemed to have no stone. However, it is well recognised from everyday clinical practice that patients with no symptoms can pass small stones. From the cohort of 116 patients who were studied, 53 were diagnosed as having no stone. We think that some patients may have had stones not identified on CT. To be able to quote a high sensitivity for spiral CT we consider a direct comparison with another imaging modality, which is the recognised gold standard with high sensitivity and specificity, or even ureteroscopy, should be undertaken to definitively exclude the presence of calculi. Whilst we accept the many advantages of spiral CT over IVU, i.e. the speed of the investigation, the ability to detect other pathologies and the increased sensitivity/specificity, we would question the accuracy of claiming a sensitivity of 98% for that investigation.