Small aortas were documented by CT in six patients, 16-34 years old. The diameter of these aortas measured at the level of 1 cm below the orifice of the superior mesenteric artery ranged from 10 to 12 mm, much smaller than the mean of 17 mm obtained from 20 subjects, 16-20 years old. Such small aortas are usually produced by vasoconstriction as a compensatory response to hypovolemic shock.