The following review examines the bacteriological characteristics, epidemiology, pathogenicity and antimicrobial susceptibility of the "Streptococcus milleri group". "Streptococcus milleri group" is a term for a large group of streptococci which includes Streptococcus intermedius, Streptococcus constellatus and Streptococcus anginosus. Usually considered commensals, these organisms are often associated with various pyogenic infections including cardiac, abdominal, skin and central nervous system infections. Organisms of the "Streptococcus milleri group" are often unrecognized pathogens due to the lack of uniformity in classifications and difficulties in microbiological identification. Penicillin G, cephalosporins, clindamycin and vancomycin all possess activity against these streptococci. Use of agents with poor activity may promote infections with "Streptococcus milleri group" and allow it to exhibit its pathogenicity. An understanding of these organisms may aid in their recognition and proper treatment.