Haemophagocytic lymphohistiocytosis (HLH) is a rare aggressive condition due to abnormal immune activation and hyperinflammatory response. It can be fatal if not treated promptly. Haemophagocytic lymphohistiocytosis frequently affects infants < 3 months of age, but it also occurs in children & adults. It can be classified as primary or secondary. Primary HLH is caused by genetic mutation and mainly occurs in the paediatric population. Secondary HLH is triggered by infections such as Dengue, Hepatitis B & C, EBV, CMV, HIV & Covid 19, and rheumatological conditions like SLE and malignancy. HLH frequently presents as pyrexia of unknown origin with pancytopenia and high transaminases. The diagnosis is mainly based on HLH-2004 criteria. Early diagnosis and early initiation of HLH-specific therapy may influence the prognosis of the disease. Definite treatment of HLH is based on HLH- 2004 protocol which includes early use of cyclosporin with corticosteroids and chemotherapy with Etoposide...