We sought to define variations in internal jugular vein (IJV) anatomy and the effect of recommended cannulation maneuvers on a population of ICU patients. Maneuvers that decreased IJV lumen cross-sectional area were carotid artery palpation (1.48 to 0.82 cm2, p less than .05) and advancement of the needle (1.57 to 0.75 cm2, p less than .001). The head-down (modified Trendelenburg) position increased IJV lumen cross-sectional area (1.18 to 1.62 cm2, p less than .05). There was wide variability in IJV anatomic features, although most patients had patent veins.