The spore-forming anaerobic bacterium Clostridium difficile has become a serious enteropathogen. Oral and parenteral administration of antibiotics can cause ecological disturbances in the normal intestinal microflora. Suppression of the normal microflora may lead to reduced colonization resistance with subsequent overgrowth by pre-existing, naturally resistant microorganisms, such as C. difficile. C. difficile infection shows a range of clinical presentations between an asymptomatic carrier state, light diarrhea without inflammatory changes, and pseudomembranous colitis. C. difficile infection is acquired by the fecal-oral or environmental-oral routes. From March 2000 through March 2001 we assessed 48 cases of nosocomial antibiotic-associated diarrhea (AAD). Of these, 21 were due to C. difficile (CDAD). Cephalosporin was the agent most commonly associated with CDAD. Avoidance of cephalosporins, strict use of "single shot" prophylaxis, isolation of infected, symptomatic patients in single-bed rooms, improved hygiene and complete room disinfection lead to a rapid decrease of CDAD. The etiology, prognosis and prophylaxis are discussed in this paper.