With improved laboratory identification procedures, Streptococcus milleri (intermedius) is becoming recognized as an important human pathogen with the potential to form abscesses in a wide range of organs. The occurrence of a rapidly progressive and toxic empyema due to this organism in an otherwise healthy young adult without a predisposing lower respiratory tract infection allows us to examine the possibility that this microbe may be a significant but frequently unrecognized cause of adult empyema.