A new technique for stereotactic radiosurgery by use of a patient rotator is described. Using the rotator with a small collimated beam of 6 MV x-rays, a small well-defined region of the brain can be irradiated to a high dose with rapid fall off of the dose outside the target volume. Since the linear accelerator gantry does not move during therapy the possibility of a collision between the gantry and the patient or stereotactic equipment is eliminated. The system is also independent of the rotational stability of the linear accelerator gantry axis and turntable axis. Dose distributions measured in a Lucite head phantom with film exhibited properties well suited for radiotherapy. Tests carried out to evaluate the ability to irradiate a selected target point within the brain with the rotator system showed a maximum positional error of 1.0 and 2.0 mm for angiography and CT localisation respectively.