To assess the relative importance of acute watery diarrhoea (AWD) and other types of acute diarrhoea as causes of morbidity and mortality among infants and 1-4 years old children, we examined 3 different data sources from the Matlab field project of the International Centre for Diarrhoeal Disease Research, Bangladesh. In infants, prevalence rates for AWD and non-watery diarrhoeas were similar. In children, prevalence of AWD was 1.8 times lower than prevalence of other acute diarrhoeas. In infants, admission rate to a diarrhoea hospital was 4.1 times higher for AWD than for other acute diarrhoeas (P less than 0.001). In children, admission rate was only 1.7 times higher for AWD than for acute diarrhoeas (P less than 0.001). Infant mortality was 1.7 times higher for AWD than for other acute diarrhoeas, but child mortality was 3 times lower for AWD. These data suggest that, while diarrhoeal disease control programmes should give more importance to oral rehydration therapy in infants, field management of the other types of acute diarrhoea should receive more emphasis in children.