Among the microorganism involved in environmental contamination, Legionella spp is actually considered an important infectious hazard. The aim of this study is to evaluate the incidence of Legionella spp in water samples collected from 138 dental unit selected from public outpatient clinics of 6 Italian cities. The samples were taken from oral rinsing cup, air-water syringe, ultrasonic scaler and the turbine to investigate Legionella spp, Pseudomonas aeruginosa and the total heterotrophic count at 36 degrees and 22 degrees. Legionella spp was present in 33,3% dental unit water; but a significant difference was shown among the enrolled cities. In 43,5% of water sample Legionella concentration was 1.000-10.000 CFU/L and in 30,4% was >10.000 CFU/L. L. pneumophila 1 was found in 23,9% of water samples. The results demonstrate that the concentration of Legionella spp in dental unit water lines could be high and this suggests that the exposure to these micoorganism during the dental practise could be a potential health risk both for dental personnel and for the patients too, especially when immunocompromised.