During 1997 a large dengue epidemic occurred in Rio Grande do Norte, a State in north-east Brazil. The co-circulation of dengue virus type 1 and dengue virus type 2 was demonstrated by virus isolation in Aedes albopictus clone C6/36 cell-line and by reverse transcriptase-polymerase chain reaction (RT-PCR). IgM capture enzyme-linked immunosorbent assay confirmed 52.3% of the 8105 studied cases and dengue antigen was demonstrated by immunohistochemical reaction on hepatocytes from 2 out of 5 fatal cases studied. Individual risk factors for development of dengue haemorrhagic fever/dengue shock syndrome, such as hypertension, diabetes mellitus and bronchial asthma, are discussed.