The number of children dying worldwide of diarrhoea fell by a third between 2005 and 2015, researchers have found.
The Lancet study says better access to clean water and sanitation is key, with fewer weak and malnourished children becoming infected.
New vaccines have also had a positive impact.
However, diarrhoea is still the fourth-biggest killer of children globally, with almost 500,000 a year dying before their fifth birthday.
This figure could well be a significant under-estimate because of the lack of data in sub-Saharan Africa, where most cases occur.
Preventable and treatable Diarrhoea is also indirectly responsible for large numbers of deaths, through exacerbating the effects of other diseases, such as pneumonia and measles.
The US researchers, who analysed data from the new Global Burden of Disease study, found well over a third (42%) of deaths happen in Nigeria and India.
Diarrhoeal diseases, such as rotavirus and cholera, are spread by water contaminated with faeces. They are preventable and treatable.
"Diarrhoeal diseases disproportionately affect young children," said lead author Dr Ali Mokdad, from the Institute for Health Metrics and Evaluation at the University of Washington.
"Despite some promising reductions in mortality, the devastating impact of these diseases cannot be overlooked."
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