We report the case of paraneoplastic vasculitis of the central nervous system associated with breast cancer. A 54-year old woman had a complete workup because of recidive seizures. Magnetic resonance imaging (MRI) showed cerebral and medullary cryptogenic lesions, and a diagnosis of encephalomyelitis of unknown origin was made. She was treated with corticosteroids, but because of cognitive impairment and recurrence of epileptic seizures, she was finally transferred to our Neurology Department. The previous diagnosis was then changed, because a poorly differentiated invasive lobular breast cancer was discovered. Thoracic and abdominal computed tomography (CT) scans diagnosed pulmonary, pericardial, adrenal, and renal metastases. Because MRI findings did not fit with the diagnosis of brain metastases, a CT-guided cerebral biopsy was performed, and she was eventually diagnosed with paraneoplastic vasculitis of the central nervous system.