Stereotactic radiosurgery is a controversial treatment modality in the management of cerebral cavernous hemangiomas (CHs), and results vary from center to center. Even the interpretation of treatment failure is controversial. It is suggested that the systematic pathological investigation of irradiated specimens could help to resolve the controversy. A hemorrhagic lesion in the posterior part of the thalamus had been diagnosed as a tumor and was treated with 40-Gy fractionated radiotherapy. One year after this treatment the case was reconsidered based on new imaging evidence, and the lesion was removed by conventional craniotomy. Histopathological examination revealed a CH with postirradiation changes. Compared with nonirradiated control CH tissue samples, there was endothelial cell destruction and marked fibrosis with scar tissue formation in the stroma of the treated lesion. The histopathological findings in this specimen were similar to those described in arteriovenous malformations after gamma knife surgery. The results of light microscopic investigations suggest that the ionizing effect of radiation energy evokes vascular and connective tissue stroma changes in CHs as well.