BACKGREOUND: When a double-lumen endotracheal tube (DLT) is used for one-lung ventilation, its position should be accurate. But only a few studies has been performed about how to predict the depth of insertion for DLT preoperatively. The purpose of this study is to investigate which physical measurements are correlated with the depth of insertion for left-sided DLT and how the depth of insertion for DLT can be explained with these physical measurements. METHODS: After placing a 5 cm-high pillow under the patient's head, we intubated left-sided disposable DLT (BronchocathTM, Mallinckrodt medical Ltd, USA) in 65 adults. We tape-measured sternocleidomastoid muscle (SCM) length and sternal length. We positioned the proximal margin of the bronchial cuff of DLT just below carinal bifurcation through fiberoptic bronchoscope, and recorded the depth of insertion for DLT at the upper incisor level. RESULTS: The depth of insertion for DLT was correlated with both height (y=3.96+0.15x, r2=0.51, p=0.0001) and SCM length (y=16.73+0.82x, r2=0.49, p=0.0001). Sternal length (r2=0.11, p=0.0081) was weakly correlated with the depth of insertion for DLT. The best regression model was depth of insertion for DLT (cm)=6.88+0.09 height (cm)x0.46 SCM length (cm). CONCLUSIONS: The depth of insertion for DLT is correlated with SCM length as well as height. So we may use them in predicting the depth of insertion for DLT.