This article aims to give a comprehensive description of cardiac resource utilization in adults at a freestanding children's hospital. Retrospective chart review. Large, tertiary, freestanding children's hospital. Adults (18 years of age and older) seen within the heart center or evaluated by heart center personnel from January 1, 2006 through December 31, 2010. There were 2794 adults that utilized cardiology services during the study period. The mean patient age was 23.5 ± 8.4 years (18-70.5). The 1748 (62.6%) patients had a diagnosis of congenital heart disease. There were a total of 525 catheterization laboratory encounters and 104 cardiac surgical procedures performed on adult patients during the 5-year study period. The in-hospital mortality for all invasive encounters was 0%. The minor adverse event rate for all invasive encounters was 6.7% and 4.8%, respectively. Also, the overall major adverse event rates were 1.9% and 4.8%, respectively. There were 162 cardiology evaluations performed on adults in the emergency room. There were a total of 5489 adult cardiology clinic visits. The most common congenital heart disease diagnoses were: tetralogy of Fallot: 228 (13%), D-transposition of the great arteries: 208 (11.9%), single ventricle physiology: 187 (10.7%), atrial septal defect 128: (7.3%), and ventricular septal defect: 117 (6.7%). Overall, the complexity of congenital heart disease was: simple: 41%, moderate: 37%, and complex: 22%. A significant and growing number of adult patients are currently being cared for at pediatric institutions. Excellent outcomes have been achieved at these centers with dedicated adult congenital heart disease services, consisting of both cardiologists and other faculty trained in adult medicine. Others with training in adult medicine, whether they be staff or contracted consulting services, are also required to help manage adult comorbidities.