BACKGROUND: Anaerobic bacteria can cause various infections, and their incidence may differ greatly, depending on the country or hospital. We investigated recent trends in anaerobe isolation and clinical characteristics of anaerobic bacteremia in one hospital in Korea to facilitate diagnosis and treatment of anaerobic infections. MATERIALS AND METHODS: Anaerobic bacteria isolated from blood, body fluids and abscess specimens at a university hospital in Korea during 2007 and 2008 were analyzed. The medical records of 82 anaerobic bacteremia patients were reviewed. A retrospective cohort study was conducted to determine the risk factors for in-hospital mortality of patients with anaerobic bacteremia. RESULTS: A total of 289 non-duplicated anaerobic isolates were recovered from blood, body fluids and abscess specimens. Bacteroides fragilis (73 isolates, 25.3%) was the most common organism followed by Clostridium perfringens (22 isolates, 7.6%), Peptoniphilus asaccharolyticus (21 isolates, 7.3%) and Anaerococcus prevotii (19 isolates, 6.6%). Eighty-four isolates were recovered from blood specimens, among which B. fragilis (24 isolates) and C. perfringens (21 isolates) were the most frequently isolated organisms. Among the 196 underlying diseases of anaerobic bacteremia patients, neoplastic, infectious, and gastrointestinal diseases accounted for 54 (27.6%), 46 (23.5%), and 41 (20.9%) cases, respectively. The alimentary tract was the most common suspected portal of entry. The in-hospital mortality rate of anaerobic bacteremia patients was 34.2%, and neutropenia at the time of blood culture was the only statistically significant factor associated with mortality in this study. Anaerobes were isolated in 1.4% of all positive blood cultures. CONCLUSIONS: B. fragilis and C. perfringens are expected to be commonly isolated from clinical specimens. Despite its low prevalence, anaerobic bacteremia displays a significant in-hospital mortality rate. Ongoing investigations into anaerobic bacteremia are necessary because of ambiguous risk factors for mortality.