A relationship between infective endocarditis and colon cancer was established in 1950, and Streptococcus bovis was successfully isolated in 1970. However, this association and its pathogenesis still remain unclear. In this paper, we describe the clinical case of a patient with a history of colon cancer and infective endocarditis caused by Streptococcus bovis. The role of S bovis as an aetiological agent in the development of colon cancer is intriguing but uncertain. S bovis infection should be considered a silent sign of gastrointestinal malignancy or hepatic disease. We believe that in order to demonstrate the presence of colon cancer, all patients with S bovis infection require an endoscopic investigation of the colon.