The aim of this work was to offer a description of the clinical manifestations developed by patients under 1 year who had dengue virus infection and dengue hemorrhagic fever during the epidemic which broke out in 1981, and to determine if the passive transfer of maternal dengue antibodies to the fetuses influenced the occurrence of a severe development of the disease, through a retrospective study. In 20 cases, type 2 dengue virus infection was confirmed. Eight patients showed the clinical manifestations of dengue hemorrhagic fever of dengue shock syndrome (DHF/DSS), and the other 12 had the typical dengue virus infection. The former were of the white racial phenotype, aged under 6 months. There was a predominance of type 1 dengue antibodies in the mothers of children with DHF/DSS. Fever, rash, vomiting and diarrheas (not frequent) appeared in the two clinical manifestations of the infection; blood leukocytes were predominantly lymphocytic; and erythrocyte sedimentation was always normal. Patients with DHF/DSS presented with some bleeding (87.5%); cyanosis and ascites (37.5%); and shock (25%), as well as hepatomegaly. All these infants with DHF/DSS had thrombocytopenia and most of them showed hemoconcentration. No deaths occurred.