Background: Acute febrile illness is a non-specific term used differently in clinical and public health contexts. Research on the etiology of Acute febrile illness is important in directing appropriate empiric treatment and case management, prioritizing resources, developing prevention and control measures, identifying novel pathogens and outbreaks, and supporting global health security goals. Methods: During 2019-2020, physicians screened patients of 1 year in outpatient departments in private hospitals. Patients with high fever were randomly enrolled in Yatharth hospital, Gautam Buddha Nagar, Greater Noida, Uttar Pradesh, India during assessment with onset within past 14 days. Results: This study involved 175 hospitalized patients with fever, with a median age of 39 years and 58% males. The majority of cases were undifferentiated, with only 30.2% having a specific cause for the fever such as enteric fever or viral fever. Respiratory tract infection was the most common non-malarial AFI, followed by urinary transmitted infection. Patients aged 31-45 years made up the highest percentage of cases. Conclusions: Different age groups showed trends in laboratory parameters, including mean hemoglobin values and mean PCV count. Patients with underlying comorbidities showed deviations in lab investigations, with diabetes and CAD having elevated GGTP, SGOT & SGPT levels, and CKD and COPD having greater mean RDW (%) values. Tuberculosis and CKD were associated with anemia. Tuberculosis and CKD were associated with anemia.