Radiation-induced cavernous malformations are rarely reported, and most cases have been children. We describe two adult patients with cavernous malformation after irradiation for astrocytoma. Magnetic resonance (MR) imaging, at their ages of 53 years, showed a cavernous malformation in the irradiated field 26 and 10 years after resection and irradiation, respectively. Cavernous malformations were confirmed by the histopathological examination in the both cases. Radiation-induced cavernous malformations are rare in adult patients with astrocytoma. One reason why we found two such cases was that these patients had been successfully treated for astrocytoma and had long follow-up periods.