['To demonstrate an asymmetry of the internal jugular veins, a finding which will have consequences for catheterization.', 'Prospective study.', 'The medical ICU of a university-affiliated teaching hospital.', 'Eighty critically ill consecutive patients.', 'Measurement of the cross-sectional area of the internal jugular veins. Search for an asymmetry, defined as an area at least twice that of the contralateral vein.', 'An asymmetry was noted in 62.5% of the patients. The dominant vein was the right in only 68 % of these cases. In addition, 23% of the 160 jugular internal veins had an area of 0.4 cm2 or less.'] Are the Internal jugular veins asymmetric . Usefulness of ultrasound before catheterization?