Dengue fever was detected in Yucatan in 1979. Since then, about 17,000 clinical cases have been reported, of which 1169 were confirmed by the presence of specific antibodies (IgM and IgG) and/or virologic studies; 10 of the cases were classified as dengue haemorrhagic fever and four died. The disease is endemic in the region and serotypes 1, 2 and 4 have been observed. This paper describes a patient with chronic autoimmune thrombocytopenic purpura who developed a primary dengue infection with hemorrhagic manifestations and responded to corticosteroids. We discuss the physiopathogeny of thrombocytopenia and analyze the utility of treatment with corticosteroids in patients with autoimmune disease.