Risk factors for pneumonia were analysed in a large population of critically ill patients, collected in two prospective multicentre "pneumonia studies" in Italy. Twenty-three intensive care units were involved and the study time was 150 unit months. Only patients without previous pulmonary infection, with intensive care unit stay greater than or equal to 48 hours and no rapidly irreversible illness at admission were included. The incidence of pneumonia in the 1475 selected patients was 15% (220 cases). 239 patients died in ICU; the mortality rate was significantly higher in patients developing pneumonia (p less than 0.0001); pneumonia was found to be an independent highly significant risk factor for death in critically ill patients (OR = 3.88; p less than 0.0001). Multivariate analysis of seven risk factors for pneumonia showed a significantly higher risk in patients with neuromuscular disease (OR = 3.8, p less than 0.002), impairment of airway reflexes at admission (OR = 2.93, p less than 0.0001), and greater than or equal to 24h respiratory assistance (OR = 3.05, p less than 0.0001). Impairment of airway reflexes at admission to the emergency room or intensive care unit identifies the population who will experience 3/4 of the overall lower respiratory tract infections. Rapid recognition of at-risk patients seems clinically important and may improve awareness programs and preventive approaches.