The incidence of brain abscess in congenital heart disease marks 4-6%. Of these, tetralogy of Fallot is the most common congenital heart disase. We had experienced 2 cases of brain abscess associated with tetralogy of Fallot among 32 cases Of brain abscess from March -'57 to September-'74. Case 1;A 10 years old boy was admitted to our hospital in March-'66 because of headaches and vomiting. He had a history of Potts' operation under the impression of tetralogy of Fallot at the age of 5. Findings of clinical examination and diagnostic studies gave us an impression of a huge cystic mass in the right posterior temporo-occipital area. We aspirated about 80cc of pus, but no microoraganisms were noted on direct smear and culture. Case 2;A 7 years old boy was admitted to our hospital in August-'74 because of headaches and fever. He had been suffered from tetralogy of Fallot from the age of 3 without any surgical intervention. We made a burr hole on the right anterior temporal area under the impression of right posterior fronto-temporal mass, and aspirated about 15cc of pus. Multiple Gram positive cocci were noted on direct smear, but nothing on culture.