Abstract: A computer controlled stereotoxic radiotherapy system is disclosed which facilitates a precise localization and subsequent irradiation of small intracranial tumors. The system permits the accurate integration of the diagnostic and therapeutic procedures utilized in connection with intracranial tumors, including precise determination of space coordinates of the tumor and the repetitive repositioning of the patients's head in space within a scanner and/or accelerator coordinate system. The system is uniquely designed for fractionated repetitive radiotherapy but may be used in other medical fields such as surgery and radiology.