OBJECTIVE To determine whether adults with congenital heart disease have adequate knowledge of infective endocarditis and endocarditis prophylaxis and to ascertain whether an educational program effectively improves patient knowledge and compliance. METHODS We asked 102 consecutive patients to complete a 12-question survey to assess their knowledge of heart disease, infective endocarditis, and endocarditis prophylaxis. RESULTS Of 102 patients, 100 (98%) completed the questionnaire. Sixty-eight patients knew the name of their heart disease. Fifty patients correctly defined endocarditis, but only 43 knew hygiene measures that could prevent endocarditis. Ninety-six patients knew that they needed to take "a medicine" before dental procedures, and 76 of those patients (79%) knew that an antibiotic was necessary. Patient use of cardiac medications and a history of endocarditis correlated significantly with knowledge of endocarditis. Patients who had been to the Adult Congenital Heart Disease Clinic at least once knew endocarditis prevention measures and the importance of regular dental and cardiology follow-up significantly more frequently than did first-time attendees. Despite educational counseling, however, patient recall of endocarditis and its prevention is disappointing. CONCLUSIONS Many adults with congenital heart disease have inadequate knowledge of their cardiac lesion, endocarditis, and endocarditis prophylaxis. Educational efforts for adults with congenital heart disease need to be updated and reinforced regularly.