Two cases with delayed radiation necrosis of the chiasmatic region following irradiation of the hypophysis for treatment of Cushing's disease were presented. Case 1 was a 36-year-old female who had reduction of visual acuity and bitemporal hemianopsia 2 years after 60Co-irradiation therapy (total 8000 rads) for Cushing's disease. CT scans showed low density in the pituitary fossa and irregular contrast-enhanced suprasellar mass, and metrizamide CT cisternography revealed the pituitary fossa filled with contrast medium. From those findings, secondary empty sella syndrome was suspicious. Case 2 was a 35-year-old male who had progressive visual disturbance 3 years after 60Co-irradiation therapy (total 9050 rads) for Cushing's disease. The right visual acuity was 0.05 and the left one was 0.1. Examination of visual field showed left homonymous hemianopsia. CT scans showed the contrast enhanced suprasellar mass extending to the right anterior thalamic region, and metrizamide CT cisternography detected secondary empty sella as same as that of Case 1. Both cases were treated by administration of steroid hormone intrathecally and orally which was not effective. Right frontotemporal craniotomies were performed. Intraoperative findings of the chiasmatic region revealed diffuse adhesions and thickening of arachnoid membrane with mesh-work of fine vascular proliferations and adhesiotomies were performed in both cases. On the postoperative course, visual disturbance did not improved in both cases. Histological examinations of the thicked arachnoids obtained intraoperatively showed the fibrous connective tissues with round cells infiltrations in both cases, and in Case 2, the small vessel in the arachnoid was occluded by organized thrombi. Authors reviewed and analyzed literatures of delayed radiation necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)