Steptococcus suis is a Gram-positive, facultatively anaerobic coccus that has been implicated as the cause of a wide range of clinical disease syndromes in swine and other domestic animals. In swine, the disease has spread worldwide but is more prevalent in countries with intensive swine management practices. The disease syndromes caused by S. suis in swine include arthritis, meningitis, pneumonia, septicaemia, endocarditis, polyserositis, abortions and abscesses. S. suis has also been implicated in disease in humans, especially among abattoir workers and swine and pork handlers. In humans, S. suis type 2 can cause meningitis, which may result in permanent hearing loss, septicaemia, endocarditis and death. The pathogenic mechanism of S. suis is not well defined. Several virulence factors have been identified, but their roles in pathogenesis and disease have not been well elucidated. Much work is in progress on characterization of virulence factors and mechanisms, with emphasis on the control of the disease. Because of the non-availability of suitable immunoprophylaxis, control of S. suis infection has depended mainly on the use of antimicrobials.