An experimental study to measure the velocity profile within aneurysms has not been previously reported, although some theoretical works have been done. In the present studies, measurements of the velocity and pressure waveforms within model aneurysms have been done using a constant temperature hot film anemometer and a high frequency pulsed directional ultrasonic Doppler. A vein grafted aneurysm model was used in this investigation. Turbulent flow was detected at the neck and body of aneurysms. Pressure waveforms were compared between aneurysms and the parent vessel. The results suggest that turbulence evidenced by the distorted flow and high pressure pulse waves may plan an important role in the growth and rupture of a cerebral aneurysm. The mechanisms of the growth and rupture of a cerebral aneurysm are discussed.