The Red List of Threatened Species says populations of more than half of mammalian species are falling, with Asian primates particularly at risk.
The biggest threat to mammals is loss of habitat, including deforestation.
But there is good news for the African elephant, whose recovery leads to removal from the high-risk list.
This year's Red List looks at 5,487 mammals, and concludes that 1,141 are currently on the path towards disappearance.
This may be an under-estimate, the authors caution, as there is not enough data to make an assessment in more than 800 cases. The true figure could be nearer to one- third.
"Within our lifetime, hundreds of species could be lost as a result of our own actions, a frightening sign of what is happening to the ecosystems where they live," said Julia Marton-Lefevre, director-general of the International Union for the Conservation of Nature (IUCN) which publishes the Red List.
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