Objective. Color Doppler ultrasonography is the most widespread diagnostic procedure in obstructive disease of the arteries supplying the brain. To our knowledge, there are only a few correlative color Doppler ultrasonographic and angiographic studies of the vertebral arteries, especially in patients who have flow-restrictive stenosis at the carotid bifurcation. The main purpose of this prospective study was to, evaluate diameter, flow volume, and time-averaged mean velocities of angiographically verified normal vertebral arteries without collateral flow. The second purpose was to, try to establish a threshold value for the flow volume of the vertebral artery. Methods. One hundred twenty patients referred for carotid angiography with a normal vertebrobasilar system and with no patent posterior communicating arteries were investigated with color Doppler ultrasonography. Luminal diameter, time-averaged mean velocity, peak systolic velocity, and flow volume values were calculated for each patient. The parameters were compared between sexes, in different age groups, in patients with carotid stenosis of 50% or less and greater than 50%, and in patients who had clinical signs of vertebrobasilar insufficiency versus those who had not. Results. We have found no significant difference in evaluated parameters with the degree of associated. carotid stenosis or vertebrobasilar insufficiency. Diameter and flow volume values on the left side were, higher than on the right side. Conclusions. We found similar flow volume values of vertebral arteries in both sexes and both groups of patients with carotid stenosis of 50% or less and greater than 50%. All parameters did not differ in patients with stenosis of 50% or less and greater than 50% and in patients with and without clinical signs of vertebrobasilar insufficiency.