Operating theatres are among the hospital’s most risky environments as far as infections are concerned. Surgical site infection is a serious complication of surgery, associated with increased morbidity, mortality and costs. The ambient air of the operating theatre represents an important vehicle of micro-organisms causing surgical site infection, in particular in clean operations. The aim of this paper is to give a brief historical excursus of the milestones of the prevention of airborne surgical site infections. The debated issue on the use of unidirectional airflow ventilation system is presented. Some national recommendations for threshold air microbial contamination values are reported, and the need for a European standard on air quality to provide a safe operating theatre environment for surgical patients is underlined.