The clinical course, neuro-imaging features and neuropathologic findings in a child with para-infectious acute cerebellar swelling are described. Reversible transtentorial and transforaminal herniations occurred and required emergency posterior fossa decompression with external ventricular drainage. Neuropathologic examination of a cerebellar biopsy demonstrated a subacute pathogen-free cerebellitis. Following neurosurgical intervention and steroid therapy, symptoms and signs resolved and the patient is well 3 years later. Acute para-infectious cerebellar swelling is potentially fatal unless recognised and treated early in its evolution.