Streptococcus bovis is a relatively frequent causative agent of endocarditis or bacteriaemia, particularly in the elderly. In the past S. bovis has often been incompletely or even falsely classified. For therapeutic and prognostic reasons it is important to classify this agent exactly with biochemical methods even in the routine laboratory. Endocarditis or bacteriaemia due to S. bovis are often seen in conjunction with malignant, potentially malignant or benign colorectal neoplasias. After endocarditis or bacteriaemia due to S. bovis thorough investigation of colon and rectum is indicated. On the other hand, in presence of fever in patients with colorectal tumors, S. bovis bacteriaemia or endocarditis must be considered. The available literature is inconclusive on the question whether, after S. bovis endocarditis or bacteriaemia with initially normal colorectal findings, examination of the upper gastrointestinal tract and periodic inspection of the colon is needed. Up to now there has been no satisfactory explanation for the concomitant occurrence of endocarditis or bacteriaemia due to S. bovis and colorectal neoplasia.