The number of adults with congenital heart disease (CHD) is increasing. However, rates of health care resource utilization in this population are unknown. The objectives of this study were to describe the use of general health care resources in adults with CHD and to examine the impact of CHD severity on resource utilization. The study consisted of adults alive in 1996 who had > or = 1 diagnosis of a CHD lesion conforming to the International Classification of Disease, Ninth Revision, in the physician's claims database of the province of Quebec from 1983 to 2000. From 1996 to 2000, rates of health care utilization were measured. The impact of the severity of CHD on the use of health care resources was determined using multivariate models to adjust for age, gender, Charlson co-morbidity score, and duration of follow-up. The study population consisted of 22,096 adults with CHD (42% men). From 1996 to 2000, 87% received outpatient care from specialists, 68% visited emergency rooms, 51% were hospitalized, and 16% were admitted to critical care units. Patients with severe CHD had higher adjusted rates of outpatient cardiologist care (rate ratio [RR] 2.24, 95% confidence interval [CI] 2.06 to 2.45), emergency department utilization (RR 1.09, 95% CI 1.03 to 1.17), hospitalization (RR 1.30, 95% CI 1.19 to 1.43), and days in critical care (RR 2.12, 95% CI 1.80 to 2.50) than patients with other congenital cardiac lesions. Hospitalization rates were higher than in the general Quebec adult population (RR 2.08, 95% CI 2.00 to 2.17). In conclusion, adults with CHD have high rates of health care resource utilization, particularly those with severe lesions. Appropriate resource allocation is required to serve this growing population.