Lack of saliva in the mouth leads to the endangerment of oral and general health, and to the reduction of life quality. The aim of this graduation thesis was to review the most common causes and consequences of lack of saliva in order to emphasize the importance of saliva presence in the mouth. Patients subjectively experience reduction in the amount of saliva or change in its quality as a dry mouth or xerostomia. The causes that lead to it can be associated with diseases of the salivary glands, systemic diseases, iatrogenic external factors or other reasons, such as dehydration or tobacco smoking. Regardless of the cause, dryness of the mouth leads to serious consequences, such as rapid development of caries, inflammation of the oral mucosa and salivary glands and, along with it, an uncomfortable feeling in the mouth, bad breath and speech, chewing and swallowing dysfunction. Due to the increasing number of patients, especially the elderly, who complain of dry mouth, it is important to be aware of the causes and consequences of xerostomia so that they could be given the appropriate support.