BACKGROUND Few data exist about buildup of secretions within endotracheal tubes of patients treated with closed-system suctioning in the intensive care unit. OBJECTIVE To describe the extent, prevalence, and distribution of narrowing of endotracheal tubes related to buildup of secretions and to determine contributing factors. METHODS Forty endotracheal tubes were examined within 4 hours of extubation, after at least 72 hours of use. Data on patients' daily weight and fluid balance, ventilator humidification temperatures, and nurses' descriptions of secretions during the 3 days preceding extubation were recorded. Any secretion debris in the endotracheal tubes was weighed. At 1-cm intervals along the tube, the debris was described and the depth of the debris was measured to the nearest 0.5 mm. RESULTS Mean duration of intubation was 6.6 days. Two tubes had no debris. Mean overall depth of debris was 0.64 mm, mean greatest depth was 2.0 mm (range, 0-5 mm), and mean weight was 1.16 g. The entire tube was affected, with the greatest depth of debris at the 6- to 9-cm and 13- to 14-cm markings. Duration of intubation correlated with mean greatest depth of debris (r = 0.37, P = .02), mean overall depth of debris (r = 0.48, P = .002), and mean weight of debris (r = 0.38, P = .02). CONCLUSIONS Endotracheal tubes are markedly narrowed by the buildup of secretions after closed-system suctioning. Duration of intubation, but not endotracheal tube size or amount of secretions, was associated with the degree of narrowing.