Although the association between Streptococcus bovis endocarditis and colon carcinoma is well known, very few cases of S. bovis infection associated with underlying malignancies have been reported in Korea. The S. bovis group has been recently reclassified and renamed as Streptococcus gallolyticus and Streptococcus infantarius subspecies under a new nomenclature system. We report a case of infective endocarditis with colon cancer caused by S. gallolyticus subsp. gallolyticus (previously named S. bovis biotype I). A 59-yr-old woman presented with a 1-month history of fever. Initial blood cultures were positive for gram-positive cocci, and echocardiography showed vegetation on mitral and aortic valves. Antibiotic treatment for infective endocarditis was started. The infecting strain was a catalase-negative and bile-esculin-positive alpha-hemolytic Streptococcus susceptible to penicillin and vancomycin. The strain was identified as S. gallolyticus subsp. gallolyticus with the use of the Vitek 2 GPI and API 20 Strep systems (bioMerieux, USA). The 16S rDNA sequences of the blood culture isolates showed 100% homology with those of S. gallolyticus subsp. gallolyticus reported in GenBank. The identification of the infecting organism, and the subsequent communication among clinical microbiologists and physicians about the changed nomenclature, led to the detection of colon cancer. The patient recovered after treatment with antibiotics, valve surgery, and operation for colon cancer. This is the first report of biochemical and genetic identification of S. gallolyticus subsp. gallolyticus causing infective endocarditis associated with underlying colon cancer in a Korean patient.