In order to update global estimates of diarrhoeal morbidity and mortality in developing countries, we carried out a review of articles published from 1980 to the present and calculated median estimates for the incidence of diarrhoea and diarrhoeal mortality among under-5-year-olds. The incidence of diarrhoea obtained (2.6 episodes per child per year) was virtually the same as that estimated by Snyder & Merson in 1982, while the global mortality estimate was lower (3.3 million deaths per year; range, 1.5-5.1 million). The mortality estimate is based on a small number of active surveillance and prospective studies, and thus associated with a large degree of uncertainty, reflecting the weakness of the global database. However, many surveys reporting reductions in mortality in several locations are consistent with a decreased estimate for mortality. More accurate execution of WHO survey methods, including population-based sampling in representative locations, and repeat surveys every 5 years, are needed to monitor the progress of diarrhoeal disease control programmes and trends in diarrhoeal morbidity and mortality over time.