Abstract Background: Urinary calculus remains to be a common presentation in the hospital. It is the third most common urological problem after urinary tract infection and prostate disease with life time prevalence of urolithiasis at 10-15%.The prevalence has risen over a 20-year period from the mid 1970's to the mid 1990's. The diagnosis of urolithiasis is largely dependent on analyzing the clinical presentation and physical examination. Suspicion is confirmed with radiologic tests, particularly the multidetector computed tomography scan. The advent of multidetector computed tomography has not only provided detection and confirmation of calculi, but also accurate detection of its size and location. Aim of Study: In this study, we explore the diagnostic utility of KUP and CT scanogram attenuation value of a stone to predict its appearance in Plain KUP radiograph in the hope to decrease the need for an additional CT of patients. Patients and Methods: This was a retrospective study was conducted at Radiodiagnosis Department in Ain Shams University. It included patients diagnosed to have urolithiasis after undergoing CT scanogram with a typical clinical picture of suspected urinary calculi such as flank pain and/or hema-turia. Patients included in this study must have concurrent or follow-up plain kidneys; ureter and urinary bladder radiograph. The duration of the study ranged from 6-12 months. Results: This study conducted on 60 cases with age ranged from 19 to 64 years and with mean±SD of 44.48±12.02; they were 24 females (40.0%) and 36 males (60.0%) with total 118 stones, the visible 65 (55.1%) and not visible 53 (44.9%) of scout-CT. The visible 66 (55.9%) and not visible 52 (44.1 %) of KUB X-ray, the ranged size 1-90 with median 7.55 (4-15) and the ranged density “hounsfield" 50-1700 with median 657 (400-1100). Conclusion: The cut-off value at which urinary calculi not identified by CT Scout, but KUB radiographically opaque is set at >600, with sensitivity of 84.85% specificity of 82.69%, and Scout-CT which was >689, with sensitivity of 81.54% specificity of 92.45%, The CT-scout film with an optimal HU cut-off value, when utilized together, can further aid clinicians in deciding the plan of management for patients with urolithiasis.