Introduction: Early diagnosis and risk prediction of severe dengue are necessary, especially in high case burden areas. In order for early detection of severe dengue, frequent clinical and laboratory parameters are measured in all patients admitted to the hospital with dengue infection, posing a huge cost to the healthcare. The purpose of the study is to look whether persistence NS1 antigen, using rapid bedside test, can be used to predict dengue severity among adult dengue patients. Methods: Adults with suspected dengue fever, presented to Emergency Department of Universiti Kebangsaan Malaysia Medical Centre were recruited in the study. Serial clinical and laboratory parameters were taken in patients, including rapid NS1 antigen. Clinical outcomes of each patient were determined, including severe dengue. Results: From the total of 66 patients recruited with positive NS1 antigen in earlier phase, 12% (n=8) developed severe dengue. There was no correlation noted between persistence NS1 antigen beyond day 5 of illness and severe dengue (P value 0.519). Conclusion: Our study did not show a statistically significant relationship between a persistent level of NS1 antigen beyond day 5 of illness and severe dengue. Further study, with a higher number of study populations will need to be performed to determine the relationship between persistence NS1 antigenaemia and dengue severity.