Background: Psychiatric symptoms have been reported in adult patients with dengue fever (DF); however, information on pediatric patients remains inadequate. We sought to identify the prevalence and determinants of depression and anxiety and identify other encephalopathy symptoms among pediatric and adult patients with DF.Methods: This cross-sectional study used a non-probability purposive sampling method among clinically or serologically confirmed in-patients with DF. Participants completed the Revised Child Anxiety and Depression Scale for pediatric patients and youth controls and Hospital Anxiety and Depression Scale for adult patients. Results: The prevalence of depression and anxiety were significantly higher among 225 pediatric patients than among 81 youth controls, but was lower than that among 43 adult patients. A multiple linear regression analysis of socio-demographic and clinical data found that age, family history of DF, ≤2 days of hospitalization, and myalgia and arthralgia tended to increase depression and anxiety scores of pediatric patients. Further, 26.7% of pediatric patients reported irritability, agitation, visual hallucinations and aggressiveness. Conclusion: Prevalence and determinants of depression and anxiety and the presence of encephalopathy symptoms differ between pediatric and adult patients. Longitudinal post-DF recovery studies should be conducted to examine whether these symptoms may develop to subsequent chronic psychiatric conditions in the future.