One of the most frequent complications of antibiotic therapy is a diarrheal syndrome, which may be related both to the direct toxic effects of antibiotics on the gastrointestinal tract, and the activation of conditionally pathogenic intestinal flora. Particular attention gets to present the problem of C. difficile-infection, which may be the consequence of the development of pseudomembranous colitis in both children and adults. The article presents current data on the prevalence, etiology, pathogenesis of antibiotic-associated diarrhea, as well as various clinical variants of klostridial infection. In the light of modern approaches to prevention and treatment of this pathology attention paid to the possibility of using probiotic preparations based on S. boulardii.