The objective of this study was to verify the incidence of nosocomial pneumonia in intubated and extended mechanically ventilated patients having endotracheal suctioning by an open vs. closed suction method aiming to decrease nosocomial pneumonia. Twenty-four (51.1%) patients received open-tracheal suction and 23 (48.9%) received closed-tracheal suction. The inclusion criteria were: surgical and medical patients older than 13 years, undergoing mechanical ventilation for more than 48 hours. Additional data were gathered using the Acute Physiology and Chronic Health Evaluation II, and details on smoking, alcoholism, diabetes mellitus, renal failure, previous lung disease, and previous use of antibiotics, steroids, H2 antagonists and antacids. Among the 24 patients having open-tracheal suction, 11 developed nosocomial pneumonia while of the 23 patients undergoing closed-tracheal suction, seven developed infection (P = 0.278). Risk factors for nosocomial pneumonia were not significantly different between the two groups. In the final logistical regression model the following variables remained: groups (open and closed) [odds ratio (OR) = 0.014; confidence interval (CI) = 0.001-0.416; P = 0.014] and use of prior antibiotics (OR = 2.297; CI = 1.244-4.242; P = 0.008). Use of a closed suction system did not decrease the incidence of nosocomial pneumonia when compared with the open system. The exogenous risk factors were the most important for acquiring this infection.