BACKGROUND Although Streptococcus intermedius has been recognized as an important pathogen for abscess formation outside the central nervous System, the Streptococcus milleri group, of which it is a member, has not been recognized as a specific pathogen for brain abscess, often thought to be caused by Streptococcus viridans, which includes other streptococcal species. METHODS Two cases of brain abscess in the left frontal lobe caused by S. intermedius, which responded well to antimicrobial treatment combined with needle aspiration, are presented. In the first patient, the predisposing disease was paranasal sinusitis of the frontal and ethmoid sinuses. In the second patient, the source of the pathogen was not detected despite extensive examination. The patients underwent aspiration of pus under ultrasound guidance in the first patient, and via a computed tomography-guided stereotactic procedure in the second patient. They subsequently received appropriate antimicrobial therapy against S. intermedius isolated from the pus culture. Both patients were discharged without any neurological deficits. CONCLUSIONS It is important to recognize S. intermedius as a pathogen of brain abscess, and to be aware of its predisposing factors, i.e., mucosal disturbance and liver abscess.