A 21-year-old woman presented with an acute febrile illness after a two-week holiday in Jamaica. Her symptoms started two days after return, with sudden onset of continuous high fever (> 39 degrees C), dizziness and nausea. Three days later she developed a generalized macular rash, which led to the tentative diagnosis "acute dengue fever." Laboratory confirmation was achieved by demonstrating anti-dengue IgM and IgG antibodies in paired sera; in addition, flavivirus particles were directly visualized by electron microscopy.