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The role of Streptococcus bovis (S. bovis) as an aetiological agent in the development of colorectal cancer (CRC) is intriguing but uncertain. A relationship between infective endocarditis (IE) and CRC was established by McCoy and Mason in 1951 and, for the first time, an association between S. bovis and endocarditis was successfully recognized by Watanakunakorn in 1974. In the same year, Hoppes and Lerner hypothesized that some previous reports of endocarditis caused by penicillin-sensitive “enterococci”, including that of McCoy, were probably unrecognized examples of S. bovis. In 1977, Klein and coworkers showed the prevalence of S. bovis in fecal cultures from patients with S. bovis septicemia and carcinoma of the colon was significantly increased. Thus, S. bovis infection should be considered a silent sign of gastrointestinal malignancy. Over the past 50 years, several case reports and studies – most retrospective – have been publishing on this topic often producing contradictory results. Currently, only Streptococcus gallolyticus subspecies gallolyticus (SGG) – formerly known as S. bovis biotype I – has been recognized to be directly related to colonic neoplasia. Hence, in order to demonstrate the presence of a colon cancer, all patients with S. bovis/gallolyticus infection would require an endoscopic investigation.