Purpose: To assess effects of an automated kilovoltage selection tool on radiation dose, tube current, and image quality in pediatric contrast material-enhanced thoracoabdominal computed tomography (CT) and CT angiography. Materials and Methods: The institutional review board approved this retrospective study of 87 children (median age, 10.5 years; age range, 1 day to 19 years) who underwent thoracic CT, abdominal CT, or CT angiography with an automated kilovoltage protocol between November 2010 and July 2011. Volumetric CT dose index (CTDIvol) and milliamperage were compared with estimated prescanning calculations from a standard 120-kVp protocol. Image quality was subjectively scored on a scale of 1 to 5. In 15 patients who underwent scanning with both automated kilovoltage and standard 120-kVp protocols, image contrast and noise were quantitatively measured and the contrast-to-noise ratio (CNR) was calculated. Parametric and/or nonparametric testing of independent and/or paired samples was performed. Results: Estimated median CTDIvol for all 87 studies was 4.8 mGy for the automated kilovoltage protocol versus 7.1 mGy for the 120-kVp protocol, yielding a 27% dose reduction (25% and 75% percentiles: 23% and 37%, respectively; P < .001). The median milliamperage was 125.0 with the automated protocol and 87 with the 120-kVp protocol (P < .001). Use of automated kilovoltage selection resulted in kilovoltage reduction from 120 kVp in 82 of the 87 patients (94%), with the percentage dose reduction greater for CT angiography than for chest CT (P < .001). Reduction in kilovoltage showed a significant correlation with patient size (P < .01). Diagnostic image quality was achieved in all patients. Mean contrast and noise were higher with the automated kilovoltage protocol than with the 120-kVp protocol (P ≤ .04), but CNRs for liver and portal vein were similar (P = .54 and .73, respectively). Conclusion: In pediatric CT and CT angiography, the use of automated kilovoltage selection technology significantly reduces radiation dose while maintaining image quality and CNR.