Although monitoring of blood velocity in the cerebral arteries with transcranial Doppler ultrasound is standard practice, methods for fixation of the ultrasound probe to the skull continue to impose a technical challenge. This report describes a novel method of probe fixation in which an inexpensive polymer block is custom-made for each patient to hold the probe at a fixed angle. In addition to comfort and durability, its major advantage is that the polymer block prevents dislodgment of the probe from the intended angle by forces of gravity or by patient movement. Thirty-one temporal windows were monitored with this technique, with stable signals obtained in all subjects despite aggressive movements. Disadvantages include the inability to insonate more than one vessel and the cost for each block. However, the method is quick, is relatively inexpensive, and provides significant advantages of probe stability.