In recent years an increase in the number of Clostridium difficile- associated diarrhoea cases has been reported worldwide. This is due mainly to the increasing number of elderly patients being admitted to hospitals, changes in hygiene standards and changes in the antibiotics used to combat other diseases. But changes in the virulence of C. difficile strains also seem to play a role. This review presents the current knowledge of C. difficile-associated diarrhoea in the light of these changes in incidence and virulence.