Three Australian tourists who recently travelled to islands in the Gulf of Thailand developed febrile illnesses associated with myalgias, thrombocytopenia, and atypical lymphocytosis. Dengue 1 virus was isolated from all three patients. The patients' clinical features and serological and virological investigations are presented. These cases highlight the need for awareness of dengue amongst travellers and the preventive precautions required when visiting endemic regions. After the urgent exclusion of malaria, dengue should be considered in the differential diagnosis of febrile persons who have recently returned from endemic regions.