Stereotactic radiotherapy utilizing a linear accelerator has been investigated. (1) Radiosurgery, (2) fractionated stereotactic radiotherapy, and (3) fractionated radiotherapy followed by stereotactic boost have been performed according to pathology, size, and prognosis of diseases. Accuracy in localization of the treatment center was within one millimeter using a CT simulator. From July, 1990 to December 1992, 69 lesions in 63 patients have been treated using the stereotactic radiotherapy according to prospective dose-escalation design. Five patients have experienced transient worsening of nerve palsy or headache, but these complications were self-limited. No late radiation damage was observed over a mean follow-up period of 12.5 months. Encouraging improvements were obtained in patients with metastasis, AVM, and acoustic neurinoma although the follow-up period was too short to be conclusive. Stereotactic radiotherapy utilizing a linear accelerator is thus suggested as a safe and effective approach providing that dose-volume-time relationship is well controlled.