In September, 2010, a 21-year-old woman, who worked as a waitress at an Italian restaurant, presented to our neuro-logical department with a sudden-onset, non-specifi c headache of moderate severity, which was unresponsive to over-the-counter medications. She also had vomiting and unsteadiness. 2 weeks before she had had a self-limited episode of febrile gastroenteritis. On admission, she was afebrile and she had horizontal nystagmus. Blood tests showed slight leuco cytosis. Over the next 24 h, her neurological status worsened and she developed mild neck stiff ness, bilateral cerebellar ataxia, and right-sided facial hypoaesthesia. After 48 h, she had dysphagia, dysarthria, and persistent hiccupping. MRI of the brain showed large brainstem and cerebellar lesions with patchy regions of gadolinium enhancement and relevant oedema (fi gure). Cerebrospinal fl uid (CSF) analysis showed: protein concen-tration 1·38 g/L, glucose concentration 2·26 mmol/L, leucocytes 10/μL (70% poly morphonuclear). Oligoclonal bands were absent and CSF Gram staining negative. Molecular and serological tests for herpes simplex virus, cytomegalovirus, Epstein-Barr virus, entero virus,