A study performed on Peruvian children <10 years of age and their controls showed that Campylobacter jejuni is a leading cause of diarrhoea. Infants 1 year old or younger were the most affected. The disease was usually moderately severe, although >50 per cent of patients required I.v. fluid therapy. Campylobacter was also more frequent in malnourished patients, who come from socio-economically deprived groups, with overcrowding, poor sanitation, and frequent contact with domestic birds and animals. The seasonal behaviour suggests that diarrhoea caused by Campylobacter is endemic in this area. © 1993 Oxford University Press.