The quality of dental unit water is of great importance since patientsand dental staff are regularly exposed to water from aerosols generated during work. The main purposeof this investigation was mycological evaluation of dental unit waterlines (DUWL). The author determinedthe number and species of fungi present in the water from a unit reservoir which is the source of waterfor a dental unit, in the water flowing from a high-speed handpiece of a unit, and in the swab samplecollected from the wall of a waterline connecting a unit reservoir and dental handpieces. The followingmould fungi were identified: Aspergillus amstelodami, Aspergillus fumigatus, Aspergillus spp. from Aspergillusglaucus group, Aspergillus repens, Citromyces spp., Geotrichum candidum, Penicillium aspergilliforme,Penicillium pusillum, Penicillium turolense, Sclerotium sclerotiorum; yeast-like fungi: Candida albicans,Candida curvata and other yeasts. Some of them, in certain circumstances, especially in people with immunologicaldisorders, may be a cause of opportunistic infections. Thus, it is necessary that the DUWL should besubmitted to a decontamination protocol and to routine microbial monitoring to guarantee an appropriatequality of water used in dental treatment.