They are disappearing in these areas because their habitats are being destroyed by tropical forest clearing.
The good news is fewer are being caught for the pet trade and medical research.
The number of monkey species - or primates - in danger of dying out has gone up hugely in the last three years.
Helping plants grow
In 2000, 120 different primate types were thought to be in danger. That's risen to 1995 in just two years.
Primates are vital for the environment because they help keep important plants growing.
When they eat fruits and other plant food, the seeds are spread around the forests when they go to the toilet.