We simulated needle paths based on the central landmark used for central venous catheterization of the internal jugular vein. We obtained ultrasound images to quantify the landmark's accuracy (precision and bias) in 107 subjects placed in Trendelenburg position with their heads turned 30-35 degrees. We also determined the frequency of simulated carotid artery puncture. The simulated needle path missed the middle 80% of the lumen of the internal jugular vein in 34% of subjects (95% confidence interval [CI], 25% to 44%) and traversed the carotid artery in 26% of subjects (95% CI, 18% to 35%). Both events occurred in 20% of subjects (95% CI, 13%-29%). The landmark had a medial bias of 3.7 mm (95% CI, 2.7 to 4.8); it was more often (77 of 104 subjects) medial to the center of the right internal jugular vein (P < 0.001). The landmark was more likely to miss the internal jugular vein (odds ratio, 3.11; P < 0.016) and intersect the carotid (odds ratio, 3.03; P < 0.024) in obese patients. The central landmark should not be expected to yield frequent success on first needle pass without risk of carotid puncture because of its imprecision and bias. The measured bias should be considered when the central landmark is used for central venous catheterization.