Sure - the IRS does not normally ask for a dependent's birth certificate. Just be sure that you are entitled to claim the child as your dependent - if you are not the custodial parent then in most lilkelihood you can not claim the child as your dependent. If you want more specifics post back with a few more details, such as whether the chld lives with you, do you provide the majority of the child's support, and is there any reason to think that the child's mother may claim the child as her dependent.