With a computerized program system for stereotactic brain operations it becomes possible for the first time to react even before running a possible risk, e.g., in case of punctures in the midbrain, the brain stem, or in the hypothalamus, by simulating the operative procedure even before starting the operation itself. This is effected by the ability to change the penetration angle of the electrode or by choosing a different point of trepanation. The inclusion of computerized axial tomography, especially through the presentation of the CT scan, made to measure with the help of the linear transformation, and of the input of the cranial and ventricular coordinates through a digitizer, together with the coordinates resulting from the X-ray picture, brings the definition of the target point to a still greater optimum. Thus the safety and the precision of the stereotactic operation have been improved even further.