In order to assess the epidemiological and clinical characteristics and changing nutritional status of infants suffering from acute diarrhoea, 103 infants with such diarrhoea and the same number of age-matched controls were investigated at the Universidade Federal do Rio Grande do Norte's Paediatric Hospital, in north-eastern Brazil. Each child with diarrhoea was given oral rehydration or, in the severe cases, intravenous rehydration. Each subject was checked for enteropathogens and his or her weight, height and weight-for-height, weight-for-age and height-for-age Z-scores were evaluated immediately after any clinical dehydration had been corrected and 30 days later. In the infants aged <6 months, a diet that included foods other than breast milk (odds ratio=9.41), including one in which breast milk was supplemented with other foods (odds ratio=4.69), was found to be statistically associated with diarrhoea. The enteropathogens found most commonly in the children with diarrhoea were rotavirus (36.9%), enteropathogenic Escherichia coli (11.6%) and Shigella (11.6%). Just four (5.2%) of the 77 cases with adequate follow-up showed persistent diarrhoea. At presentation or as soon as any clinical dehydration had been corrected, the infants with diarrhoea had significantly lower weights and weight-for-height and weight-for-age Z-scores than the controls. Thirty days later, however, the weight-for-height and weight-for-age Z-scores of the cases had increased significantly, to the point when they were not significantly different from the baseline values for the controls. The negative consequences of diarrhoea on weight-for-height and weight-for-age Z-scores and the recovery of these parameters after 30 days with rehydration reflect the acute but reversible influence of diarrhoea on infant nutritional status.