AbstractWe report the case of a 9 year-old boy, presenting with an acute encephalitis with cerebrospinal fluid pleiocytosis. MRI showed T2/FLAIR (fluid attenuated inversion recovery) hyperintense signals of basal ganglia and cortex, EEG (electro encephalogram) showed diffuse slowing with epileptic discharges. A repetitively elevated IgM/IgG serologic response against Mycoplasma pneumoniae was observed with polymerase chain reaction in serum and cerebrospinal fluid remaining negative. No other pathogen or antigen could be identified. High IgG and IgM levels against the glycolipid galactocerebroside were detected in serum but not in CSF. After treatment with corticosteroids, the patient fully recovered. Brain MRI and EEG investigation returned completely normal. Besides a primary infection of the central nervous system, M. pneumoniae is associated with a parainfectious encephalitis in children which may be mediated by antibodies to galactocerebroside.