The smallest known monkey is the pygmy marmoset. It is about 14-16cm in size (without the tail). It weighs about 120 grams. It lives in the treetops of rainforests in Brazil, Colombia and Ecuador. The largest known monkey is the mandrill. It can grow to about 1 m in size. Adults weigh up to 35 kg. The monkeys often climb with the help of their tails.