Acute Encephalitis like illness (AES) is a public health problem in Uttar Pradesh. A major cause was Japanese Encephalitis (JE) but this is less frequent now. Sensitivity and specificity of neuroimaging features of JE are not known. Objective: To compare clinical and neuroimaging features in children having JE and non-JE AES. Methods: Hospital based surveillance for JE was ongoing. Standard WHO definitions were used for JE. Magnetic resonance imaging (MRI) was done whenever possible. Clinical

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... d MRI features were compared between JE and non-JE. Those in whom serology was equivocal or not done were excluded. Polymerase chain reaction was done for Herpes simplex virus-1 DNA in CSF. Results: Over a period of 2 years, 63 patients were proven JE (31) or non-JE (32) and could have MRI scan done. None tested positive for HSV-1. Focal deficits and extrapyramidal features were significantly more frequent in JE. Condition at discharge was significantly worse in JE with higher rate of focal deficits, abnormal posture and movements, inability to walk, speak and feed. Signal intensity alterations (SIA) on MRI were significantly more common in thalamus, midbrain and temporal areas, but not in basal ganglia, in JE, specificity of these findings for JE were higher than sensitivity. None of the non-JE patients had temporal lobe involvement. Conclusion: MRI changes of JE in children are confirmed although sensitivity was not high and basal ganglia involvement was infrequent. Temporal lobe changes may be seen in JE. Abstract Keywords: Magnetic resonance imaging, Acute encephalitis syndrome, Japanese encephalitis.