This report describes an epidemic of dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS) in the North Arcot Ambedkar district and the adjoining districts in Tamil Nadu and Andhra Pradesh. Nineteen children who fulfilled the clinical criteria for the diagnosis of DHF/DSS were admitted to the Christian Medical College Hospital, Vellore, during June through November, 1990. The clinical presentation was similar to that described in South-east Asian children and the case fatality rate was 26.3 per cent. Serology was confirmatory or suggestive of recent dengue virus infection in 16 children, uninterpretable in 2 and not consistent with recent dengue virus infection in 1 child. All children over 1 yr of age had very high antibody titres suggesting a secondary response whereas infants had lower titres consistent with primary response. The occurrence of recurrent epidemics in this region in the last few years with associated high case fatality emphasizes the urgent need for public health measures to curtail further epidemics.