The normal intracranial structures are relatively resistant to therapeutic radiation, but may react adversely in a variety of ways and the damage to nerve tissue may be slow in making its appearance and once damage has occurred the patient recovers slowly and incompletely. Therefore, it is important to consider the possibility of either recurrent tumor or late adverse effect in any patient who has had radiotherapy. The determination of morphological/pathological correlation is very important to the therapeutic radiologist who uses CT scans to define a treatment volume, as well as to the clinician who wishes to explain the patient's clinical state in terms of regress, rogression, persistence, or recurrence of tumor or radiation-nduced edema or necrosis. The authors are obtained as following results; 1. The field size (whole CNS, large, intermediate, small field) was variable according to the location and extension of tumor and histopathologic diagnosis, and the total tumor dose was 4,000 to 6,000 rads except one of recurred case of 9,100 rads. The duration of follow up CT scan was from 3 months to 5 year 10 months. 2. The histopathologic diagnosis of 9 cases were glioblastoma multiforme (3 cases), pineal tumor (3), oligodendroglioma (1), cystic astrocytoma (1), pituitary adenoma (1) and their adverse effects after radiation therapy were brain atrophy (4 cases), radiation necrosis (2), tumor recurrence with or without calcification (2), radiation-nduced infarction (1). 3. The recurrent sysptoms after radiation therapy of brain tumor were not always the results of regrowth of neoplasm, but may represent late change of irradiated brain. 4. It must be need that we always consider the accurate treatment planning and proper treatment method to reduce undesirable late adverse effects in treatment of brain tumors.