© 2017 The Societies and John Wiley & Sons Australia, Ltd Heterologous secondary infections are at increased risk of developing dengue hemorrhagic fever (DHF) because of antibody-dependent enhancement (ADE). IgG subclasses can fix and activate complement and bind to Fcɣ receptors. These factors may also play an important role in the development of ADE and thus in the pathogenesis of DHF. The aim of this study was to analyze the indices of anti-dengue IgG subclasses in adult patients with febrile and hemorrhagic dengue in the acute phase. In 2013, 129 patients with dengue fever (DF) and 57 with DHF in Veracruz, Mexico were recruited for this study and anti-dengue IgM and IgG determined by capture ELISA. Anti-dengue IgG subclasses were detected by indirect ELISA. Anti-dengue IgG2 and IgG3 subclasses were detected in patients with dengue. IgG1 increased significantly in the sera of patients with both primary and secondary infections and DHF, but was higher in patients with secondary infections. The IgG4 subclass index was significantly higher in the sera of patients with DHF than in that of those with DF, who were in the early and late acute phase of both primary and secondary infection. In conclusion, indices of subclasses IgG1 and IgG4 were higher in patients with DHF.