BACKGROUND: Endobroncheal intubation or extubation may occur accidentally when the patient's neck is flexed or extended even in the appropriate endotracheal intubation. The purpose of this study is to examine the effect of fixation or unfixation of the endotracheal tube at the teeth level on the displacement of its distal end when the patient's neck is extended or flexed. METHODS: This study was conducted in 37 patients who underwent endotracheal general anesthesia. The patients with the evidence of pathology in head, neck and chest were excluded from the study. Individual patient's displacement in endotracheal tube tip compared unfixed cases with fixed cases when the change of neck position. The moved distance was measured by fiberoptic bronchoscope. The data were statistically analyzed by Student's paired t-test. RESULTS: The endotracheal tube moved away from the carina when the patient's neck was extended, while it moved toward the carina when flexed in all cases. When the patient's neck was extended the average distance displaced 1.2 0.7 cm in fixed cases and 1.1 0.9 cm in unfixed cases. when the neck was flexed, they were 1.2 0.5 cm and 1.0 0.8 cm respectively. There were not statistically significant between the fixed and the unfixed cases. CONCLUSIONS: It is concluded that the displacement of the endotracheal tube is not related to its fixation or unfixation at the teeth level and therefore, unfixation does not provide any benefits in terms of the displacement of the distal end of the tube in adult trachea.