With more patients with hypoplastic left heart syndrome (HLHS) palliated through surgical revision and surviving into adulthood, long-term performance of the right-sided structures in the systemic position has become a clinical concern. Aortopathy, progressive dilation of aortic root, is one of such problems. Aortopathy in patients with HLHS is becoming a legitimate issue as it is related to aortic regurgitation, aortic dissection, and potential ventricular dysfunction, which might require surgical re-intervention. Although pathophysiology of aortic root dilation in patients with HLHS is largely unknown, several aspects of HLHS are considered to be related to the pathogenesis, such as anatomical, genetic, and hemodynamic factors, which will be described in detail in this chapter. Further elucidation of risk factors for progressive aortic dilation in HLHS as well as its mechanisms is required to establish disease-specific and stratified approach, as no specific recommendations for the management of aortic dilation in HLHS are currently available.