The purpose of this paper is to discuss the operative treatment of chronic encapsulated abscess of the brain and to report the results of operation in a small series of abscesses of this type. In view of the high mortality, any method of operation for brain abscess should be carefully scrutinized to exclude technical errors, which may not only prevent the eradication of a localized suppuration, but actually spread the infection to uninvolved regions of the brain. It is generally appreciated that the principles utilized in the successful treatment of abscess in other regions of the body must be radically modified in operations for brain abscess. An unfailing adherence to these principles in the treatment of the various types of abscess of the brain will often convert a walled-off, more or less quiescent lesion into a rapidly fatal septic encephalitis, the most frequent terminal complication of an unsuccessful operation for