OBJECTIVE Infective endocarditis accounts for 4% of admissions to a specialized unit for grown-up congenital heart patients. This study defines lesions susceptible to infection, antecedent events, organisms, outcome and surgical treatment in a group of such patients. RESULTS The grown-up congenital heart disease database was searched for all patients aged 13 years and above with adequate documentation of infective endocarditis retrospectively between 1983-1993 and thereafter between 1993-1996. There were 185 patients (214 episodes) divided into Group I: 128 patients unoperated or palliated and Group II: 57 patients after definitive repair and/or valve repair/replacement. In Group I, the commonest affected sites were ventricular septal defect in 31 (24%), left ventricular outflow tract in 22 (17%) and mitral valve in 17 (13%) and in Group II, left ventricular outflow tract in 20 (35%), repaired Fallot in 11 (19%), and atrioventricular defects in eight (14%). Infective endocarditis was not seen in secundum atrial septal defects before or after closure; in closed ventricular septal defects and ducts without left-sided valve abnormality; in isolated pulmonary stenosis; in unrepaired Ebstein: or after Fontan-type or Mustard operations. Surgery was performed in 39 patients: as an emergency in 17, and for failed medical therapy in 22. Only 87 (41%) of patients had a predisposing event: dental procedure or sepsis were the commonest events in Group I (33%) and cardiac surgery in Group II (50%). Streptococci species were found in 54% of Group I patients and in 45% of Group II. Staphylococci aureus was commoner in Group II (25%) compared to Group I (14%). Mean time from the onset of symptoms to diagnosis was 60 and 29 days in Groups I and II, respectively. Eight (4%) patients died as a result of septicaemia related to emergency or repeated surgery and Staphylococcus aureus infection. Recurrent attacks occurred in 21 (11%) patients. CONCLUSIONS Reparative surgery does not prevent endocarditis except for closure of a ventricular septal defect and duct. Delay in diagnosis is serious since it contributes to mortality, although the overall mortality % is not high. Specific lesions are not affected so prophylaxis is probably unnecessary in those anomalies.