Stereotactic radiosurgery is used to treat benign tumours, but its long-term effects are not fully understood. Here we describe a vestibular schwannoma that underwent malignant transformation 6 years after gamma knife radiosurgery applied to the tumour remnant after a primary resection. Histological specimens of the original specimen did not show any atypical features. Genotyping showed a TP53 mutation in the recurrent tumour, which did not exist in the original tumour. Our results suggest that radiosurgery induced the malignant transformation, and we propose a cautious application of this treatment for benign tumours.