STUDY OBJECTIVES: We confirm the ability of the self-inflating bulb to indicate endotracheal tube position in children and determine which method of bulb compression is more accurate. METHODS: This single-blind, prospective, single cohort, repeated measures comparison of the on-deflate and the off-deflate methods of bulb compression was conducted in the operating room of a children's hospital. Seventy-five patients weighing more than 20 kg were enrolled. All patients had an endotracheal tube placed in both the trachea and the esophagus, 5 mL/kg of air was insufflated into the stomach, and 4 measurements were obtained on each patient. The bulb was either applied to the endotracheal tube and then compressed (on-deflate method), or compressed before its attachment to the endotracheal tube (off-deflate method). The order in which the methods were utilized was determined by a computer-generated permuted block randomization scheme. The blinded assessor told the anesthesiologist when to start and stop the clock after each intervention. Five seconds was used as the cut-off time for which the clock was stopped. If the bulb reexpanded within 5 seconds, then the tube was considered to be in the trachea; if it did not reexpand, then this was considered to be an esophageal intubation. RESULTS: The mean patient age was 11 years. The on-deflate method had a sensitivity of 99% and a specificity of 92% for detecting tracheal intubations. The off-deflate method had a sensitivity of 99% and a specificity of 100% (95% confidence interval [CI] for the difference between methods: sensitivity -6 to 6, specificity -14 to 0.4). The inaccuracy rate for the off-deflate method was 1%, whereas the inaccuracy rate for the on-deflate method was 5% (Delta4; 95% CI 0.2 to 9). CONCLUSION: The self-inflating bulb is a reliable method of detecting endotracheal tube position in children. Furthermore, the off-deflate method may be more reliable and accurate than the on-deflate method when used in children weighing more than 20 kg.