Background: Acute encephalitis syndrome (AES) is defined as the acute-onset of fever and a change in mental status (including signs and symptoms such as confusion, disorientation, delirium or coma) and/or new-onset of seizures (excluding simple febrile seizures) in a person of any age at any time of the year. The clinical definition of AES was introduced to facilitate surveillance for Japanese encephalitis (JE), mosquito-borne viral encephalitis. Most AES is considered to be due to a viral-encephalitis, virus like West Nile, Herpes simplex virus, Flaviviruse like JE and dengue are more prevalent in South East Asia. Various subsequent studies confirmed that most AES in India are due to JE, which has been considered as the only major cause of AES in India. Aim: this study was conducted for a better understanding and to determine the clinical profile and outcome of AES in hospitalized children and also to determine the etiology in all cases of AES. Material and Methods: This Cross-sectional, observational study was done the Department of Pediatric, Anugrah Narayan Magadh Medical College and Hospital, Gaya, Bihar, for 13 months. Children between age 1 month to 15 years with the acute onset of fever and a change in mental status such as confusion, disorientation, coma or inability to talk and/or new onset of seizures (excluding simple febrile seizure) were included in study. All cases were investigated Cerebrospinal Fluid (CSF) analysis, dengue serology, radiological investigation as per clinical presentation. Results: out of 120 AES cases most of them were above 10 years of age (35.83%). Majority of them were males 77(64.17%), and 43(35.83%) were females. Most of the cases were reported during monsoon period 69(57.5%), followed by post-monsoon 39(32.5%) and premonsoon 12(10%). Out of 120 cases, all had fever; 89 (74.17%) had altered sensorium ; 71 (59.17%) had convulsion; 32 (26.67%) had headache; 49 (40.83%) had vomiting. On fundus examination 39 (32.5%) showed papilledema. Out of 120 cases 65(54.17%) had viral etiology, 29 (24.17%) had dengue, 7 (5.83%) had malaria, 5 (4.17%) bacterial etiology, 7 (5.83%) had tuberculosis, 6 (5%) had other causes. Those patients who had shock and need inotropes showed significant mortality (p-value: 0.014). Also those who required mechanical ventilation had significant mortality, out of 33 patients put on mechanical ventilation 19 died which was statistically significant with p -value 0.001. Conclusion: Majority of cases were in the age-group of 1-5 years, with male predominance. The peak in occurrence of cases was during post-monsoon period (October-February).