Background: Dengue is emerging as the most common monsoon related illness in India, particularly over the last few years. It has apparently overtaken Malaria as the major cause of acute febrile illnesses. An in depth observation of its trends, will pave the way towards its control. This will help contain Dengue related morbidity and mortality. It continues to dominate the monsoon related illnesses in Mumbai. This trend is persistent and rising. Mumbai, in particular, being populous, can be a breeding hub for Aedes. This combined with extensive housing projects can lead to the exponential rise in Dengue cases. This underscores the need for focussed research. Methods & Materials: A prospective, observational study was carried out on adults (>12 years) admitted with, acute undifferentiated febrile illness (temperature > 38 degree c) within 14 days of fever. The study was conducted during 3 consecutive monsoons (June to October; 2015 to 2017) in a teaching hospital in Mumbai. Clinical examination and laboratory data was studied and analysed as per study criteria. Results: During 2015,of the 879 admitted patients with acute febrile illness,206 were Dengue and 117 Malaria. Leptospirosis (12), Enteric fever (84), and Viral Hepatitis(10) constituted the other major diagnosed infections. The rest comprised undiagnosed fevers.2016 saw a further surge of Dengue. Out of 1214 admissions for acute febrile illnesses, 369 were Dengue, whereas 135 tested positive for Malaria. The rest of the diagnosed infections were-Enteric fever (116) Viral Hepatitis (10), Leptospirosis and Chikungunya, three each. Undiagnosed fevers constituted the rest. During 2017,of the 1008 cases of AFI, till October,239 confirmed Dengue cases and 65 Malaria cases was diagnosed. Enteric fever (68), Viral Hepatitis (8) and Leptospirosis (4)comprised the rest. Undiagnosed fevers comprised the rest. Conclusion: The sudden spurt of Dengue during September and October, this year, coincided with the erratic monsoons, fluctuating temperatures, torrential rains, followed by sunny weather, contributing to the climate change. Ongoing construction added to the increased breeding sites. Though there is a rise in cases during the 3 years mortality is contained. Awareness, early reporting and effective management contributed probably. Dengue continues to be the predominant monsoon related infection warranting focussed attention.