A 52-year-old man presented with sudden onset of severe headache, fever, mental confusion and mild signs of left hemisphere dysfunction. Computed tomographic and magnetic resonance imaging findings suggested a preoperative diagnosis of subependymoma of the left lateral ventricle, which was subsequently confirmed by surgery. The neoplasm could be totally removed and the postoperative clinical course was favourable. The reported case is unusual because symptomatic subependymomas of the lateral ventricle are definitely rare, and almost invariably present with a progressive clinical course over a period of weeks to years.