CONTEXTAcute encephalitis syndrome (AES) is a public health problem in north east India with Japanese encephalitis being a major aetiology. Government of India initiated an adult JE vaccination in Assam in 2011. AIMSWe aim to study the clinical profile and outcome in adult AES and JE patients after Government's JE vaccination. SETTINGS AND DESIGNAdult AES patients from 1st May 2014 to 31 st October 2014 were included in this open label, observational, prospective study. METHODS AND MATERIALSData was collected regarding clinical history and outcome. JE confirmation was done by CSF and sera samples screened to detect JEV-specific immunoglobulin M (IgM). STATISTICAL ANALYSIS USEDData analysis was done using GraphPad Prism software version 6.0. RESULTS141 (96 males, 45 females) patients of AES, were studied. With average hospital stay of 5.87 days, 100% had fever, 99.3% headache, 56.7% vomiting, 93.6% altered sensorium, 87.2% dizziness and 51.1% had seizure. 44% AES improved, 29.07% suffered residual neurological deficit and 26.65% expired. Out of 38 patients who died, 29(76.31%) patients had a GCS ≤ 7. JE was detected in 26 patients, equivocal in 2 patients and negative in 113 patients. 14(53.84%) JE patients improved, 9(34.61%) suffered residual neurological deficit and 3(11.53%) expired. JE vaccination was present in 7(4.96%) patients. CONCLUSIONSJE positive cases have reduced in adults AES patients after Government vaccination program but vaccination coverage among the AES patients was low. Clinical presentation of adult AES patients differs from most reported paediatric AES cases. However, the mortality and morbidity of AES and JE still remains high, GCS < 7 being a bad prognostic marker.