OBJECTIVES: Despite periodic outbreaks, the causes and risk factors of acute encephalitis syndrome (AES) in children of Muzaffarpur, Bihar, India, remain unknown. We explored the correlation between AES caseload and the climate parameters. METHODS: Data for 1318 hospitalized children with AES during 2012-20 were used. The correlation between AES cases and daily climate parameters (temperature, sunshine, rainfall, humidity and wind speed) for the previous 24, 48 and 72 h were examined using Pearson's and Spearman's rank-order correlation and Poisson regression or negative binomial regression analyses. RESULTS: Most (91.8%) of the AES cases occurred during the summer season (May-July months), especially June month. Pearson's and Spearman's rank-order correlation analyses revealed that AES caseload had positive correlations with maximum (r = 0.275, ρ = 0.293) and minimum (r = 0.306, ρ = 0.306) temperatures during past 24 h and heat index (r = 0.325, ρ = 0.325) and negative correlation with humidity (r = -0.222, ρ = -0.222) and rainfall (r = -0.183, ρ = -0.183) (all p < 0.05). The correlation was consistent for the climate parameters for the past 24, 48 and 72 h. Regression analysis also documented a significant association of AES cases with daily maximum (β: 0.32-0.36) and minimum (β: 0.53-0.62) temperatures and heat index (β: 0.92-1.03) over past 24, 48 and 72 h (all p < 0.01). The number of AES cases exponentially increased when the daily maximum and minimum temperatures crossed 40°C and 31°C, respectively. CONCLUSIONS: The climate parameters, especially temperature appears to be a risk factor for AES in children. The definite aetiological role of heat for AES in children needs further exploration.