Nearly one in three primates, like monkeys, apes and chimps, are in danger of dying out, according to research by conservation groups.
The World Conservation Union says the animals are at risk because the forests where they live are being cut down to make food and medicines.
The biggest threat is in Asia where lots of monkeys are also sold as pets.
Scientists say we should be especially worried about primates because they're the closest living relatives to humans.
The research concentrates on 25 of the most endangered primate species.
It claims that even if you gathered up all the surviving members of these species they would still fit inside a single football stadium and wants more done to protect them.