Clostridium difficile is an important nosocomial pathogen and the most frequently diagnosed cause of infectious hospital‐acquired diarrhoea. Toxigenic strains usually produce toxin A and toxin B, which are the primary virulence factors of C. difficile. Some recently described strains produce an additional toxin, an adenosine‐diphosphate ribosyltransferase known as binary toxin, the role of which in pathogenicity is unknown. There has been concern about the emergence of a hypervirulent fluoroquinolone‐resistant strain of C. difficile in North America and Europe. The use of fluoroquinolone antimicrobials appears to be acting as a selective pressure in the emergence of this strain. In this review, we describe the current state of knowledge about C. difficile as a cause of diarrhoeal illness.