Diarrhoea is one of the most common adverse effects of antibiotic treatment. Sometimes it may endanger both the health and the life of the affected patient. The aetiopathogenesis of antibiotic-associated diarrhoea may differ, but in the majority of cases this is the result of antibiotic-induced quantitative and qualitative changes of the gut microbiota composition. Therefore antibiotic-associated diarrhoea is usually, in fact, a clinical manifestation of iatrogenic dysbiosis. A set of symptoms caused by an overgrowth of Clostridium difficile is a specific type of antibiotic-associated diarrhoea of increasing clinical significance, not only in patients admitted to the hospital but also in outpatients. The paper reviews the basic data on risk factors, prophylaxis, and treatment of antibiotic-associated diarrhoea, in particular Clostridium difficile-associated diarrhoea.