Cerebral vasculitis is a very rare complication after brain tumour surgery. We herein report a case and discuss the origins of this complication. A 52-year-old female was admitted because of motor aphasia due to a left frontal lobe brain tumour. The magnetic resonance imaging (MRI) study revealed a non-enhanced tumour. A partial resection of the tumour and the placement of an Ommaya’s reservoir were performed. The pathological diagnosis was an oligoastrocytoma. The patient recovered well without any neurological deficits. Post-operative radiotherapy and the intravenous injection of interferon β were performed. During these treatments, the patient showed a continued high fever. An MRI scan revealed multiple enhanced lesions in the residual tumour, thus raising suspicions about a post-operative infection. We therefore performed a tumour biopsy and the removal of the exogenous materials. The histopathological diagnosis was vasculitis in the residual tumour. The patient’s consciousness and neurological symptoms recovered quickly with the steroid treatment. Following the radiotherapy (50 Gy total), complete remission of the tumour was rapidly obtained and no recurrence was observed. Cerebral vasculitis confined to the tumour bed is an unusual complication; however, this special condition was of critical importance for a successful tumour regression in this patient.