Patients who have undergone the Fontan procedure in later adolescence and adulthood represent a unique population at risk for significant morbidity and mortality. The optimal strategy for long-term management of such patients is unknown. The aim of this study was to evaluate outcomes of patients who had undergone Fontan surgery later in life, focusing on late survivorship, mode of death, and predictors of mortality. Eighty-eight patients were identified who had their initial Fontan operation from 1973 to 2007 at ≥15 years of age. A standardized tiered contact protocol was followed to capture the recent health status of each patient; the probability of survival was 83%, 71%, and 66% at 5, 10, and 15 years of follow-up, respectively. Despite focused efforts, the modes of death were not available in 48% of the patients. A prolonged intensive care unit stay at the time of operation was the single predictor of mortality (p = 0.0123). In conclusion, this investigation highlights the significant mortality that exists in patients who undergo a Fontan procedure later in life and the difficulties in achieving standardized medical follow-up for this high-risk group of patients.