This review aimed to evaluate the contamination rate of dental unit waterlines (DUWL) with Pseudomonas aeruginosa and Legionella pneumophila in several countries in the Middle East. Literature search was conducted in databases such as PubMed, Scopus, Web of Science, and Google Scholar to gather studies published from the beginning of 2000 to 30th April 2020. Medical Subject Headings (MeSH) terms were; "Legionellosis"; "Legionnaire", "Legionellosis", "L. pneumophila", "dent", "dental", "dentistry", "Dental Unit Waterlines", "dental water", "DUWL", "Middle East", ?P. aeruginosa", "Iran", ?Turkey", "Iraq", and "Jordan". The search was independently conducted by two of the authors. Data was analyzed using Comprehensive Meta-Analysis software. Almost all studies included in this review reported a high rate of bacterial contamination of DUWL, which exceeded the current standard bacterial contamination level of <200 (CFU) mL
1 recommended by the American Dental Association (ADA). The combined prevalence of L. pneumophila from four countries (Iran, Jordan, Turkey, and Iraq) was 23.5% (95% Cl: 6.5-57.7), and the combined prevalence of P. aeruginosa was reported 21.7% (95% Cl: 7.1-50.1%). This study showed a high bacterial contamination rate of DUWL with opportunistic pathogens. So, it is recommended to prevent biofilm formation in DUWL, some measures should be extended by practical approaches allowing for water quality control and improvement on-site in the dental practices such as mobile filtration units, chlorination and disinfection chemicals.  Kulcsszavak: contamination, dental unit water lines, Pseudomonas aeruginosa, Legionella pneumophila, Middle East