The great majority of cases of Clostridium difficile infection are hospital-acquired, and the reported incidence in England and Wales has increased sixfold between 1990 and 1993, with at least 17 patients dying in a recent large nosocomial outbreak. C. difficile infection accounts for an average 3-week increased length of stay in hospital. Acquisition of a toxigenic strain of Clostridium difficile may be followed by asymptomatic carriage, diarrhoea, colitis or pseudomembranous colitis. Antibiotic treatment and older age are major risk factors for the development of symptomatic disease, but less well-defined differences in strain virulence and host susceptibility are also probably important. Accurate data on the relative risks of different antibiotics to induce symptomatic C. difficile infection are scarce, but third-generation cephalosporins are frequently implicated. New kits are becoming available for the laboratory diagnosis of C. difficile infection but many of these lack sensitivity. Oral metronidazole or vancomycin are the main treatment options but avoidance of further antibiotics should also be encouraged where possible. The role of environmental C. difficile spores, which are highly resistant to conventional disinfectants, needs to be defined. Proven strategies for the prevention of C. difficile infection are required, in particular protocols to ensure that cross-infection does not occur.