For a study, researchers sought to develop an experiment in which the patients with univentricular congenital heart disease who undergo the Fontan operation, Fontan-associated liver disease (FALD) has become a nearly universal chronic comorbidity. However, there is a dearth of information describing long-term results and the effects of FALD in this population. Data from the California registry was used to identify patients who received the Fontan operation between 1992 and 2018. A composite of codes for liver diseases was used to evaluate presumed FALD. Mortality and transplant were the main results. Survival and multivariable regression analyses were carried out. With a median follow-up of 12.6 (8.4, 17.3) years, adults made up 75.9% of the 1,436 patients who had Fontan surgery. The Hispanic population was 46.3%. Overall survival at 20 years was greater than 80%. However, Hispanic patients were at higher risk of death than White patients [hazard ratio: 1.49 (1.09-2.03), P=0.012]. Although more than 54% of patients had the liver disease by the time they were 25 years old, only 225 individuals (15.7%) had suspected FALD. When compared to patients who passed away without liver disease, FALD was associated with later mortality [median: 9.6 (6.4-13.2) years post-Fontan], P=0.02. FALD patients who got a combined heart and liver transplant had a 100% 5-year survival rate, compared to just 70.7% of those who underwent a heart transplant alone. In this population-based investigation of long-term outcomes post-Fontan, a higher all-cause mortality rate was linked to Hispanic ethnicity. Furthermore, FALD is underdiagnosed, yet the data show that as people get older, the likelihood of developing the disease rises as people get older. Despite having great posttransplant survival, FALD is linked to late mortality. It highlights the demand for post-Fontan liver surveillance measures tailored specifically for FALD patients.