BACKGROUND: This study was performed to ultrasonographically demonstrate the changes in relationship between the right internal jugular vein (IJV) and an anatomical landmark in two different head positions: neutral and rotated. METHODS: This was a randomized clinical trial. One hundred patients scheduled for elective surgery under general anesthesia with endotracheal intubation were enrolled in this study. The patients were placed in the supine position with a neutral head position and without a pillow. The apex of the triangle formed by the sternal and clavicular heads of the sternocleidomastoid muscle and clavicle was marked (AL point : anatomical landmark point). Ultrasonography of the neck anatomy was performed and the skin was marked at the central point of the IJV (US point: ultrasonography point). The other investigator measured the distance from the AL point to the US point (AL-US distance). The patient's head was then turned 30degrees to the left; the same procedure was repeated and the AL-US distance was again measured. The changes in AL-US distance were calculated. RESULTS: The AL-US distance increased significantly after 30degrees head rotation compared with that in a head neutral position. The mean +/- SD of the AL-US distance was 0.28 +/- 0.78 cm in the neutral head position and 0.83 +/- 1.03 cm in the head rotated position. CONCLUSIONS: The anatomical landmark point becomes more distant from the actual right IJV point and moves more medially after head rotation. We suggest minimizing the angle of head rotation and taking this distance into consideration when using the landmark-guided method.