Stereotaxic radiosurgery is a procedure that uses a beam of radiation as an ablative surgical instrument to destroy brain tumors (or more generally, brain lesions). The beam is produced by a linear accelerator that is moved by a mechanical gantry. Radiation is concentrated by crossfiring at the tumor from multiple directions, to reduce the amount of energy deposited in healthy tissues. Because access to and exit from the tumor is obstructed along some directions by critical structures (e.g., brain stem, optic nerves), planning the path of the beam is often difficult and time-consuming. This paper describes a computer-based planner developed to interactively assist the surgeon generate a satisfactory treatment, given the spatial distribution of the brain tissues obtained with medical imaging. This planner has been experimented on using 11 cases previously processed at the Stanford Medical Center. A dosimetric comparison with the manually generated plans for these cases was carried out. Although still limited, results indicate that automatic planning can significantly improve energy deposition. It can also shorten the overall treatment, hence reducing the patient’s pain and allowing the radiosurgery equipment to be used for more patients. Stereotaxic radiosurgery is an example of so-called “bloodless surgery.” Computer-based planning techniques are expected to facilitate further development of this safer, less painful, and more cost effective type of surgery.