This report is of the first locally acquired case of dengue fever. The diagnosis was made even in the absence of a history of travel outside Hong Kong. The patient was a 21-year-old man, who presented with high fever, leukopenia, thrombocytopenia, and elevated liver enzymes. His haematocrit revealed mild haemoconcentration but the albumin was normal throughout the course of the illness. His blood pressure remained low with no tachycardia or overt shock syndrome. The pyrexia subsided 4 days after admission to hospital and all haematological and biochemical abnormalities eventually normalised. The pathogenesis, diagnostic criteria of dengue haemorrhagic fever and dengue shock syndrome, and control of dengue infection are discussed.