Flaviviruses are significant causes of disease worldwide and can be classified serologically into several antigenic complexes. The purpose of the present study was to evaluate the effectiveness of a generic RT-nested-PCR for detection of flavivirus during a dengue outbreak in Brazil in 2008. A total of 105 serum samples were collected from patients with fatal outcome and examined by generic RT-PCR, conventional RT-PCR, and IgM serology. The generic RT-PCR confirmed 19 of 105 (18%) cases. Conventional RT-PCR performed on 105 serum samples detected 45 (42.8%) dengue virus infections. The IgM serology confirmed 44 of 102 (43.1%) cases. The infecting serotype was identified by generic RT-PCR in 19 cases (18 DENV-2 and 1 DENV-3) and by conventional RT-PCR in 45 cases (40 DENV-2 and 5 DENV-3). In addition, we analyzed the performance of the generic and conventional RT-PCRs and IgM serology on serum samples stratified by the day of onset of symptoms. Our results indicate that different methods should be included in flavivirus surveillance programs, including virological and serological approaches.