OBJECTIVE: The purpose of this study was to compare the diagnostic capabilities of standard- and reduced-dose CT in the detection of nephroureterolithiasis in children. MATERIALS AND METHODS: Forty-five patients 20 years old or younger divided into two groups weighing 50 kg or less and more than 50 kg underwent unenhanced 16-MDCT in the evaluation of acute flank pain. An investigational computer-simulated tube current reduction tool was used to produce additional 80- and 40-mA examination sets (total number of image sets=135). Three independent blinded readers ranked random images for stones (confidence scale, 1-5, least to most), hydronephrosis, noise-based image quality, and presence of nonrenal lesions. RESULTS: Compared with the standard tube current used for the original CT scans, there was no significant reduction (p=0.37) in detection of renal stones at the 80-mA setting (mean dose reduction, 67%; range, 43-81%); and at the 40-mA setting (mean dose reduction, 82%; range, 72-90%), the detection rate was significantly lower (p=0.05). At the 40-mA setting, there was no significant difference among the children weighing 50 kg or less (p=0.4). Detection of ureteral stones and hydronephrosis was not significantly different at 80 and 40 mA; however, disease frequency was low, and no definite conclusion can be made. CONCLUSION: Simulated dose reduction is a useful tool for determining diagnostic thresholds for MDCT detection of renal stones in children. Use of the 80-mA setting for all children and 40 mA for children weighing 50 kg or less does not significantly affect the diagnosis of pediatric renal stones.