A 37-year-old man was treated for lung cancer by chemo-radiation therapy. Subsequently, magnetic resonance (MR) imaging identified a ring-enhanced lesion in the left temporal lobe. Gamma knife radiosurgery was performed under a diagnosis of brain metastasis. Nevertheless, MR imaging showed regrowth of the tumor 1 year later, so radiosurgery was repeated on the same lesion. Two years after the first radiosurgery, MR imaging revealed an irregularly enhanced lesion with increasing perifocal edema in the left temporal lobe. Emergency surgery was performed under a diagnosis of impending uncal herniation. The histological diagnosis was cavernous malformation. This case demonstrates that gamma knife radiosurgery can cause radiation-induced cavernous malformation.