For many years Viridans streptococci have been considered as commensal organisms in a wide variety of sites in the human body and only regarded as significant pathogens in subacute bacterial endocarditis. However, in recent years some reports have suggested that a particular species, Streptococcus milleri, can be a virulent pathogen, producing life-threatening sepsis particularly in surgical patients. We review here our experience of this organism in 23 general surgical patients over a 3 year period, and postulate that prophylactic use of antibiotic combinations such as gentamicin and metronidazole in patients undergoing colo-rectal surgery may be a factor promoting its emergence as a significant pathogen. Patients with established sepsis due to Streptococcus milleri should be considered for long-term antibiotic therapy as part of the treatment of their abscesses.