The pygmy marmoset is the smallest monkey in the world. A large pygmy marmoset weighs about 160 grams which is pretty small for a monkey.
Pygmy marmosets are similar to other marmosets such as the common marmoset. Like their relatives, pygmy marmosets are arboreal and mostly eat tree gum with an occasional piece of fruit.
While it may be tempting to get one of these cute little monkeys as an exotic pet, one should not do so. Pygmy marmosets are wild animals and like most monkeys, they really don’t like to be kept prisoners by humans. Besides in the wild they have a complicated social life and live in groups so you would need to keep several pygmy marmosets who will drive you insane.
Pygmy marmoset on Wikipedia.
Pygmy marmoset on the Toronto Zoo website.
Is it possible to have a pygmy marmoset as a pet? on Yahoo answers.