To assess the impact of a quality improvement program on the occurrence of serious complications related to endotracheal tube misplacement and to identify risk factors, we did a before and after comparison in the adult intensive care units of a military referral hospital. All adult patients requiring endotracheal intubation during two 12-month periods comprised the study population. After the identification of a sentinel case, a retrospective review identified 278 adult patients requiring endotracheal intubation over a 12-month period. Twenty-two of these patients had at least one significant endotracheal tube misplacement; five of these misplacements (23%) were associated with serious complications (anoxic encephalopathy, atelectasis and respiratory failure, gastric aspiration, pneumothorax, and hypoxemia). In four of these patients the complications directly contributed to patient morbidity and mortality. During a subsequent 12-month period, after the initiation of a quality improvement program, 246 patients requiring tracheal intubation were prospectively studied. Of these 246 patients, 113 (46%) were identified as having at least one endotracheal tube misplacement requiring immediate repositioning. The incidence of serious complications related to endotracheal tube misplacement was significantly less during the implementation of the quality improvement program (0 of 246 patients) than during the retrospective period (5 of 278 patients). Multivariate analysis showed that a longer duration of endotracheal intubation, the lack of chemical paralysis, and the occurrence of cardiac arrest were independently predictive of endotracheal tube misplacement. These results suggest that a specific ICU quality improvement program can have a favorable impact on patient outcome.