Abstract: ObjectiveTo identify the cause of an outbreak of fever among the workers returning from Cambodia in Shaanxi province in 2007. MethodsBlood samples were taken from 70 workers returning from Cambodia to detect IgM and IgG to dengue virus, dengue virus RNA in serum of the febrile cases was amplified by RT-nested-PCR, and dengue virus isolation from serum of the febrile cases was conducted. ResultsSeven samples (including 5 samples from the febrile cases) were positive for IgM and none of the serum samples were positive for IgG by reagent from CORTEZ, and 6 samples (including 4 samples from the febrile cases) were positive for IgM by IgM kit from IBL and 13 samples (including 2 samples of the febrile cases) were positive for IgG by IgG kit from IBL. A specific DNA fragment of DEN-1 virus was amplified from serum of the index case, which was confirmed by sequence analysis. No virus was isolated by C6/36 and BHK cells. ConclusionFour imported dengue fever cases were confirmed according to the experiment results, symptoms and epidemiology history, and the index case was infected with DEN-1 virus. The serological results indicated that there was asymptomatic infection among the returned workers.