We report a case of a rapidly progressing, relapsing-remitting, steroid-responsive granulocytic encephalitis without any signs of peripheral nervous system or other organ involvement. It apparently had an immune-mediated etiology that could not be attributed to any known disease entity. A 22-year-old man presented with rapidly progressive severe neurological symptoms caused by encephalitis. Examination of the cerebrospinal fluid as well as brain biopsy showed extensive accumulation of neutrophilic granulocytes with no hints of an infectious agent. Magnetic resonance imaging revealed multiple T2/FLAIR demarcated lesions. Subsequent to a steroid pulse therapy, the clinical symptoms and imaging abnormalities improved rapidly. Ten months later, the patient experienced a disease relapse, which again responded well to steroids. Forty months after the relapse, he is currently doing well on azathioprine. This case highlights that an immunosuppressive treatment should be considered in patients with extensive neutrophilic encephalitis when no infectious agent is detected. A new immune-mediated relapsing-remitting CNS disease entity might need to be considered.