A 57-year old woman had a five-day history of cough and high fever followed by abnormal behavior and headache with signs of meningeal irritation. A cerebrospinal fluid (CSF) exam revealed polymorphonuclear pleocytosis. Streptococcus pneumoniae was cultured from the patient's CSF and serum. Clinical features and laboratory investigations supported a diagnosis of pneumococcal meningoencephalitis. After treatment with intravenous meropenem (MEPM), the patient's laboratory data improved and her neck stiffness disappeared, but a brain MRI showed white matter lesions in the bilateral frontal and temporal lobes. The patient responded to pulse therapy with intravenous methylprednisolone (1 g/day), carried out over three days: she recovered neurological function and her MRI lesions resolved. We report a case of acute meningoencephalitis caused by Streptococcus pneumoniae, mimicking acute disseminated encephalomyelitis (ADEM). We suggest that pneumococcal infection is one of the pathogenetic factors in ADEM.