A major cause of morbidity and mortality among children in developing countries is acute diarrhoea and rotavirus, a reovirus-like agent, is found to be a leading causative agent. We report here the incidence of rotavirus infection among infants and young children with gastro-enteritis treated at the Children's Hospital in Dammam, Kingdom of Saudi Arabia. One hundred and fifty children, aged between 1 and 60 months, suffering from diarrhoeal illness, were selected as the study cohort; another 150 hospitalized children of the same age group, but not suffering from diarrhoea, served as controls. Sixty-two per cent of the study children complained of watery diarrhoea and 39% of vomiting; all had mild to moderate dehydration. Seventy-two per cent had fever and 30% associated respiratory illness. Worst affected were those 7-12 months old, among whom rotavirus was detected by ELISA techniques in 39.6%, compared with 7.5% of the control children of comparable age group. We could not detect any rotavirus from control children aged over 36 months, whereas approximately 15% of the study children in this age group yielded rotavirus from the stool. The second most common pathogen isolated was Shigella ssp. It was isolated from 18.7% of children under study as against 3% of the controls.