The appearance of a new lesion several years after radiation treatment for a primary brain tumor may represent different kind of pathologies. We present a 24-year-old patient who suffered from right-sided hemiparesis and ataxic gait with a history of an operation due to left frontoparieal grade II fibrillary astrocytoma and fractioned radiotherapy. His cranial MRI study showed heterogeneous signal intensity of brain stem radionecrosis in the pons spreading through the mesencephalon and left brachium pontes. The leading diagnosis was high-grade glial tumor. The patient underwent stereotaxic biopsy and histopathological examination revealed radionecrosis. Radiation necrosis has a radiological appearance similar to various important pathologies. Tissue sampling for histopathological examination is mandatory for definite diagnosis and correct treatment of the disease.