Idiopathic granulomatous encephalitis is a rare disorder of unknown etiology, undetermined treatment, and often grave prognosis. This article describes a 4-year-old female who presented with a single focal febrile convulsion followed a few weeks later by right-sided hemiparesis. A huge infiltrative cerebral mass tumor was found which proved to be a granuloma on histologic study. Despite a thorough evaluation, including tissue studies and search for an infectious agent, no etiology could be identified, and the final diagnosis was idiopathic granulomatous encephalitis. Recurrent resections and high-dose steroid treatment failed to control the process, and the patient died of disease 6 months after presentation. Evaluation and treatment of idiopathic granulomatous encephalitis should be aggressive, and the possibility of chemotherapy and perhaps even radiotherapy should be considered if there is no response to steroids.