Background: Critical aortic coarctation is defined as the severe narrowing of the isthmic aortic lumen, representing a neonatal cardiac emergency, part of the congenital heart diseases with duct-dependent systemic circulation. Aim of the study: To assess the correlation between transthoracic echocardiography and computed tomography angiography (CTA) in the mea- surement of aortic diameters in a group of newborns diagnosed with duct-dependent aortic coarctation and/or associated hypoplastic aortic arch. Material and method: We performed a retrospective study on neonates diagnosed with duct-dependent aortic coarctation and/or associated hypoplastic aortic arch between January 1, 2015 and March 1, 2017. The studied parameters were diameters of the aorta at the level of the aortic annulus, coronary sinuses, sinotubular junction, ascending aorta, proximal and distal aortic arch, and the aortic isthmus. Measurements were obtained by transthoracic echocardiography and thoracic CTA. Results: Fifteen newborns diagnosed with duct-dependent aortic coarctation and/or associated hypo- plastic aortic arch were included in this study. There was no statistically significant difference between the two imaging methods, the T test highlighting differences only between the mea- surements of the aortic annulus (p <0.016) and coronary sinuses (p <0.008). The patients in- cluded in the study associated other cardiovascular abnormalities: persistent ductus arteriosus (100%), atrial septal defect (100%), aortic arch hypoplasia (80%), bicuspid aortic valve (73.3%). Conclusions: These methods reveal important information on the anatomy of the cardiovas- cular malformation and its impact on the clinical and paraclinical status of the patient, being fundamental for establishing an optimal therapeutic approach.