A potential complication after hybrid stage 1 palliation for hypoplastic left heart syndrome (HLHS) is retrograde aortic arch obstruction (RAAO). This can lead to increased morbidity and unplanned surgical or interventional procedures in the interstage period. This study aimed to identify potential predictors of RAAO by analyzing initial echocardiograms and angiograms before hybrid stage 1 palliation. For this study, 96 patients who underwent hybrid stage 1 palliation between July 2002 and July 2009 were reviewed, 68 of which had standard HLHS and met the inclusion criteria. The initial echocardiogram, hybrid stage 1 angiograms, and follow-up echocardiograms were reviewed. Anatomic and hemodynamic measurements were obtained by both modalities, and comparisons were made between those who developed RAAO and those who did not. Of the 68 patients, 20 (29%) had RAAO. The mean aortic root size was smaller for the patients who had RAAO (3.6 vs 4.4 mm; p = 0.036). The angiographic angle between the aortic isthmus and the patent ductus arteriosus (PDA) was significantly larger in the RAAO group (86° vs 63°; p = 0.008). The retrograde aortic arch velocities were higher in the RAAO group. Patients with RAAO have a smaller aortic root and higher retrograde velocities on initial echocardiogram. Patients with RAAO show a larger angle between the retrograde arch and PDA on angiogram. Because RAAO is an important potential complication after hybrid stage 1 palliation for HLHS, identification of predictors of RAAO may lead to improved care and outcome for patients with RAAO.