In this paper, we discussed the incidence and clinical significance of blood cultures positive for anaerobes. Anaerobic bacteria is uncommon, accounting for 0.5-13% of all positive cultures. The incidence depend on the institution. Recent findings of a multicenter prospective observational trials showed that in vitro activity of the agents directed at Bacteroides species reliably predicts outcome. When a positive anaerobic blood culture was noted, appropriate action must be taken, since negligence in this respect may seriously impair the outcome of patients.