Introduction: Dengue is one of the commonest infections in Malaysia and it is a notifi able disease. Even
though the diagnosis of classical dengue fever and dengue haemorrhagic fever can be recognized clinically, the diagnosis remains a challenge in areas where it could not be differentiated with other febrile illnesses. The aim of this study was to focus on the specifi c and consistent morphological features observed in blood fi lms of dengue infection. Materials and Methods: In all 400 cases of dengue infection serologically diagnosed in the Tengku Ampuan Afzan Hospital (HTAA) during May to October 2007, only a total of 27 cases had blood fi lms examined, and thus were included in this study. These blood fi lms were re-examined by two pathologists from HTAA. The full blood count parameters were also retrieved and studied. Results: We consistently found typical reactive lymphocytes [n= 23 (85%)] and thrombocytopenia [n=21, (77.8%)] in the cases. However, leucopenia was present only in 9 cases (33%). Conclusion: The presence of typical reactive lymphocyte is a consistent fi nding in dengue fever and thus could have a signifi cant role in supporting the diagnosis of dengue infection.