OBJECTIVES: To determine whether nurses, using the WHO/UNICEF algorithm for integrated management of childhood illness (IMCI), modified to include dengue infection, satisfactorily classified children in an area endemic for dengue haemorrhagic fever (DHF). METHODS: Nurses assessed and classified, using the modified IMCI algorithm, a systematic sample of 1250 children aged 2 months to 10 years (n = 1250) presenting to a paediatric hospital in Dong Nai Province, Vietnam. Their classification was compared with that of a paediatrician, blind to the result of the nurses' assessment, which could be modified in the light of simple investigations, e.g. dengue serology. RESULTS: In children aged 2-59 months (n = 859), the nurses were able to classify, using the modified chart, the presenting illness in >99% of children and found more than one classification in 70%. For the children with pneumonia, diarrhoea, dengue shock syndrome, severe DHF and severe disease requiring urgent admission, the nurse's classification was >60% sensitive and >85% specific compared with that of the paediatrician. For the nurse's classification of DHF the specificity was 50-55% for the children <5 years and in children with definitive dengue serology. Alterations in the DHF algorithm improved specificity at the expense of sensitivity. CONCLUSION: Using the IMCI chart, nurses classified appropriately many of the major clinical problems in sick children <5 years in southern Vietnam. However, further modifications will be required in the fever section, particularly for dengue. The impact of using the IMCI chart in peripheral health stations remains to be evaluated