BACKGROUND: During one-lung anesthesia in thoracic surgery, accurate placement of double lumen endobronchial tube(DLT) is essential. We have only a few data regarding adequate depth of DLT, especially after position change. We measured the depth of DLT and the change of depth after position change in 50 adult patients. METHODS: After endotracheal intubation with left-sided Robertshaw type polyvinyl chloride(PVC) endobronchial tube, fiberoptic bronchoscope was inserted through tracheal lumen and we positioned the proximal end of the bronchial cuff just below the carinal bifurcation. The depth of the DLT from the upper incisor was recorded, and was rechecked after position change to lateral position. RESULTS: The depth of the DLT was 29.4 +/-1.3 cm(male: 30.2+/- 0.9, female: 28.2+/- 0.8) and this was related with height. But in female group depth of DLT was not related with height. Within the same height group, the depth of DLT differ up to 3.5 cm. The change of depth more than 0.5 cm after position change ocurred in 21 out of 50 patients. CONCLUSION: The adequate depth of DLT in Korean patients, in total patients and in male group seems to related with their height, but in female group the depth of DLT was not related with their height. Within same height group, the depth of DLT may differ greatly. So, the depth of DLT must be adjusted individually. After position change, the head and neck should be kept in neutral position and the adequacy of the depth of DLT must be rechecked.