Background. As a result of the Fontan procedure, the prognosis of congenital single-ventricle heart disease has improved, with many affected children surviving into adulthood. However, the unanticipated consequences of chronic exposure to Fontan hemodynamics have revealed a new set of secondary noncardiac complications. Fontan-associated liver disease (FALD) is characterized by progressive hepatic fibrosis in nearly all patients post-Fontan, with the potential to develop cirrhosis, hepatocellular carcinoma, and the need for liver transplantation. A lack of data regarding FALD-related prognosis makes consideration of indications for and timing of heart alone versus combined heart-liver transplantation challenging. Methods. A multidisciplinary group within the American Society for Transplantation analyzed several administrative datasets to study the epidemiology of FALD. Results. This approach presented several obstacles, and efforts to characterize FALD were limited by a lack of Fontan- and FALD-specific diagnostic codes and an inability to follow individual patients through multiple health systems. Several ongoing Fontan registries were also reviewed but these do not adequately capture FALD-related variables. Such barriers highlight the need for large-scale data collection in patients post-Fontan to better understand and care for this complex population. Conclusions. This study emphasizes the challenges of studying emerging transplant-related diagnoses in existing datasets and the need for mechanisms to adapt registries to appropriately identify patients with rare or emerging conditions.