OBJECTIVES: To study the effect on total leucocyte count and their significance as well as of platelet count with serositis in patients of short duration febrile illness with NS1 antigen positivity.INTRODUCTION:NS1 ANTIGEN was used to diagnose dengue infection and various flavivirus infections. Leucopenia , a well described feature is caused by bone marrow suppression by dengue virus. Selective leakageof plasma in pleural and peritoneal cavity due to functional change in vascular integrity . MATERIAL AND METHODS: An observational study done retrospectively . Cases of febrile illness who tested positive for NS1 ANTIGEN (RDT) from the period of july 2018 to November 2018 were studied for presence of leucopenia , thrombocytopenia and serositis. RESULT: leucopenia is a common finding in NS1 positive patients. However , there was no association seen of leucopenia or thrombocytopenia with presence of serositis