We evaluated the aortic outflow tract (AOT) and coronary artery dimensions in pediatric patients with unicommissural aortic valves. A retrospective review of an echocardiographic database identified 37 patients with unicommissural aortic valves. A total of 115 echocardiograms were reviewed, and the right coronary artery (RCA), left main coronary artery (LM), left anterior descending coronary artery aortic valve annulus, aortic root, sinotubular junction (STJ), and ascending aorta were measured and z scores determined. The aortic stenosis peak gradient and the amount of aortic regurgitation (AR) were also measured. The RCA diameter (z score, 1.85 ± 1.8, p = 0.03) and LM diameter (z score, 1.74 ± 1.47, p = 0.04) are significantly dilated, as are all the AOT measurements: aortic annulus (2.02 ± 1.9, p = 0.02), aortic root (2.25 ± 1.9, p = 0.02), STJ (2.22 ± 1.74, p = 0.01), and ascending aorta (4.38 ± 2.03, p < 0.001). Longitudinal follow-up showed that there was no significant variation over time in any variable. The AOT measurements were significantly correlated with each other. A trend was found in which an increasing amount of AR gave an increase in AOT measurements. The aortic gradient was not significantly associated with any measurement. Our study population demonstrated significant dilatation of the RCA and LM as well as the AOT. The dilatation of the AOT structures is likely caused by the same mechanism that accounts for the AOT dilatation in patients with bicommissural aortic valves. Dilatation of the coronary arteries may represent an intrinsic abnormality in the vessel wall. Further studies are needed to define possible changes.