Leuconostoc spp. used to be considered nonpathogens to human, but human infections have been reported including bacteremia in compromized patients. Leuconostoc spp. may be misidentified as lactobacilli, streptococci, pediococci and enterococci due to atypical biochemical tests. Leuconostoc spp. are intrinsically resistant to vancomycin. We report a case of bacteremia caused by Leuconostoc lactis identified by 16S rRNA sequencing; the isolate was not identified by commercial kits. (Korean J Clin Microbiol 2006;9(2):137-141)