For some thirty years it has been known that pathologic proliferation oftoxigenic Clostridium difficile may lead to inflammation of colonic mucosa which, in its fully developed form, manifests as pseudomembranous colitis. CDAD (Clostridium difficile - Associated Disease or Diarrhoea) is the term which is generally and quite aptly used for the disease in literature on the subject. In most cases, the disease develops after the administration of broad-spectrum antibiotics, yet there are also other important pathogenetic factors involved which should not be ignored. The disease has grown in significance over recent years due to the occurrence of serious epidemics in a number of advanced countries provoked by a highly virulent strain characterised as ribotype 027, toxinotype III, pulsovar NAP1. CDAD is a potentially fatal disease, yet it can be effectively cured if diagnosed on time. Stool toxin testing plays a crucial role in the diagnostics of the disease, and the use of endoscopy has been on the rise. Administration of targeted antibiotics is of critical importance for successful therapy, metronidazol or orally administered vankomycine being considered the most reliable, and there are also other drugs with promising effects. However, the rate of recurrence of the disease is as high as 25%. In view of the realistic threat of propagation of the highly virulent strain in the territory of the Czech Republic, preparations have started for the setting up of a national reference laboratory for Clostridium difficile typification.