Dengue fever (DF) and dengue haemorrhagic fever (DHF) are caused by the dengue virus. The major pathophysiological hallmark that distinguishes DHF from DF is plasma leakage as a result of increased vascular permeability. Following this leakage, hypovolaemic shock occurs as a consequence of a critical plasma volume loss. Constant haematological abnormalities occurring in DHF and frequently include bone marrow suppression, leucopenia and thrombocytopenia. An enhanced immune response of the host to a secondary DV infection is a feature of DHF and leads to many consequences. These are immune complex formation, complement activation, increased histamine release and a massive release of many cytokines into the circulation, leading to shock, vasculopathy, thrombopathy and disseminated intravascular coagulation (DIC). The mechanisms underlying the bleeding in DHF are multiple. These are vasculopathy, thrombopathy and DIC. Thrombopathy consists of thrombocytopenia and platelet dysfunction. DIC is prominent in patients with shock. The most severe DIC and massive bleeding are the result of prolonged shock and cause a fatal outcome. The mechanisms of thrombopathy and DIC and the proper management of DHF are reviewed and discussed.