It is important to remember that monkeys are a type of primate as well and belong in the same groupings of very close relatives. You could say that on the chain of evolution, that they are close cousins and should be treated with respect as a member of your family. Depending on where you live, the rules and regulations on keeping monkeys as pets may differ and you may not be able to own certain typed of monkeys as pets. It is important to remember that even though they are cute as babies that some monkey can grow to very large sizes and will become very aggressive when they reach adulthood or sexual maturity.
Monkeys are very difficult to care for and need much of the same things that humans do to keep them healthy. They need clean water, healthy food, and regular checkups with a veterinarian that treats exotic animals and monkeys and much more. They are a very large responsibility and the rules and regulations regarding primates protect them higher when animal abuse is involved. You can be sure that you will have to have a permit to own a monkey and have their vaccinations in order as well as having them physically evaluated on an yearly basis to make sure that you are doing everything possible to keep them healthy both physically and mentally.
Other than all of the difficult information on how to care for them, they make a very good companion in the home. They are more like companions then pets as they are able to express emotion, give you information on how they feel and more. Owning a monkey is much like owning any other animal, but they require more attention and personal one on one time with you. They need a lot of attention to keep them stimulated and out of depression!