To compare the conventional method for cannulation of the internal jugular vein with the ultrasound-aided technique. Prospective, randomized trial. Medical and surgical patients requiring central cannulation in a university hospital. Consecutive medical and surgical patients in whom central venous cannulation was indicated. Cannulation of the internal jugular vein was performed by one anesthesiologist. During the first 6 months, the ultrasound-aided technique (n = 29) was used, and during the second 6 months, the conventional technique (n = 27) was applied. The venous lumen was reached with fewer punctures (1.2 +/- 0.5 vs. 3.3 +/- 3.0 punctures per patient) and the cannulation time was shorter (35 +/- 19 vs. 198 +/- 211 secs) while using the ultrasound-aided technique. The ultrasound-aided method showed that the large-bore (diameter greater than 2.0 mm) needles invariably perforated the medial wall of the internal jugular vein, increasing the risk of perforating the adjacent carotid artery. Ultrasound guidance reduces both the duration of time and the number of punctures required to cannulate the internal jugular vein. The Seldinger technique appears safer for catheterization of the internal jugular vein.