Background:Ultrasound (US) is a non-invasive method used for the diagnosis of urolithiasis. If the size of the stone is <5 mm, it may be difficult to diagnose. This study aimed to compare the accuracy of twinkling artifact (TA) of color Doppler US imaging with unenhanced computed tomography (CT) for detecting urolithiasis <5 mm.Materials and Methods:This prospective study was conducted on 100 patients with suspected renal calculus presented to the emergency room at the Imam Khomeini Hospital of Ahwaz in 2018. The US findings such as posterior acoustic shadowing and TA were examined for their ability to detect urinary stones (greatest diameter ≤5 mm) using CT findings as the gold standard.Results:The mean size of renal stone was 3.43 ± 0.80 mm in CT and 3.49 ± 0.82 mm in color Doppler US. There was no significant difference between CT and color Doppler US report in quantification of urolithiasis sizes (P = 0.603). TA on color Doppler US was detected in 94 (94%) patients while posterior acoustic shadow was detected in 83 (83%) patients (P = 0.004). A significant difference was found between the TA and size of stones (P = 0.036). The sensitivity, accuracy, and positive predictive values of TA for the detection of calculus were 94%, 94%, and 100%, respectively.Conclusion:The results demonstrated that TA on color Doppler US could be a good and safe alternative imaging modality with comparable results with non-contrast-enhanced computed tomography for the sensitive detection of urolithiasis <5 mm.