Clostridium difficile is a well-established cause of infectious nosocomial diarrhea in adults. Each time diarrhea is observed in a patient receiving antibiotic treatment, Clostridium colitis should be suspected; diagnosis should be confirmed by the identification of toxin in the patient's stools. Its incidence is increasing due to growing use of several classes of antibiotics, and is associated with a high relapse rate and a significant case-fatality rate. The elderly are particularly at risk for this type of infection. Recent developments include the occurrence of epidemics in restricted communities and settings and the appearence of new virulent strains of this pathogen (especially PCR Ribotype 027). Vancomycin should be preferred over metronidazole in severe cases of diarrhea. New treatments are currently being tested and evaluated. Prevention remains a priority; high standards of hygiene and careful attention to the judicious prescription of antibiotics are crucial in this regard.