Acute febrile illnesses (AFI) such as dengue, leptospirosis, and scrub typhus start with fever, but some patients can deteriorate rapidly. Identifying these patients at risk is necessary to ensure early referral. The study's objective was to assess the utility of serum adrenomedullin (ADM) as a biomarker in predicting outcomes in adult AFI patients presenting to the emergency department (ED). In this prospective observational study, all consecutive patients admitted with AFI through the ED between June 2023 and February 2024 were assessed for eligibility. Clinical and laboratory findings were noted. The serum samples sent routinely for biochemical tests were used to calculate ADM levels at admission and 48 hours later (whenever possible). Clinically relevant outcome variables were collected for all patients. The utility of ADM in predicting 7-day mortality was evaluated for primary outcome analysis using a stepwise binary logistic regression. A total of 181 patients were recruited, with dengue (n = 91, 50%) being the most common diagnosis. The median sequential organ failure assessment score at admission was 5 (IQR: 3-10). The 7-day mortality was 26 (14%, 95% CI: 9.3-19.5). The median admission ADM levels and difference in ADM levels at 48 hours were significantly higher in those who died by day 7. Adrenomedullin levels at admission were found to be an independent predictor of 7-day mortality (adjusted odds ratio: 1.002, 95% CI: 1.001-1.004, P = 0.005). High ADM levels can be used for early referral in patients with tropical AFI. There is a need to explore the utility of antibodies targeting ADM in clinical studies.