Dentists belong to a professional group potentially exposed to harmful biological factors which most often are infectious microorganisms, less frequently - allergenic or toxic microorganisms. The fundamental routes of spreading harmful microorganisms in a dental surgery are: blood-borne, saliva-droplet, direct contact with a patient and with infected equipment, and water-droplet infections. In this paper, the current status of knowledge on microbiological hazards in a dentist's work is presented. Groups of microorganisms, such as prions, viruses, bacteria, fungi and protozoa, to which a dentist is, or may be exposed, are discussed. Epidemiological assessment of microbiological hazards in a dentist's work was performed and the basic principles of prevention formulated. Special attention was given to microflora in dental unit waterlines, and the biofilm persisting in them, as a source of occupational hazards specific for a dentist's workplace.