How do you replace a car key?

Call up the dealership that is the make of your car and give them the VIN# and they will make you a key.

That is not your only option. There are many locksmiths that specialize in

automotive key "origination". I myself originate keys on a weekly basis.

The reason I am improving this answer:

Many dealerships only can go back into their system so far, so many years back -

e.g. Ford Motor Co. only goes back 10 years. Being 2011 now, if you have a 1997

model Ford, the dealer cannot help you. I know this because I go to the Ford

dealership here locally and produce keys regularly because every year they purge

the previous tenth year back from the system.

Hope this helps.

P.S. Some vehicles keys can ONLY be made at the dealer (mostly brand new cars etc). Pricing varies from place to place (even dealerships) so SHOP AROUND.