Although Enterococcus casseliflavus with intrinsic low-level vancomycin resistance has rarely been isolated from clinical specimens, this organism may cause serious invasive infections such as endocarditis and bacteremia. This low prevalence may be due, in part, to the inability of automated systems to recognize this organism. Vancomycin may not be effective against E. casseliflavus, despite in vitro results that indicate vancomycin susceptibility. It is important that all E. casseliflavus isolates obtained from clinical specimens that are related to serious infections should be identified to species level for appropriate antibiotic therapy. We report a case of bacteremia caused by E. casseliflavus in a 44-year-old female patient with liver disease. (Korean J Clin Microbiol 2001;4(2):146-149)