The IRS tracks every taxpayer through a Social Security number. When you file your own returns, this isn't a problem. But if you drop all your data off at your accountant's office, make sure your Social Security number is in there, as well as your spouse's if you file jointly.
Don't forget the ID numbers of your dependents. You'll need those numbers, too. This includes everyone you claim, from elderly parents to infants. If your kids don't have their numbers yet, contact the Social Security Administration immediately. And don't forget the tax identification number of the person or business that takes care of the children while you're at work. You'll need it if you file for the child care credit.
A missing Social Security number for any person listed on your return could cost you. The IRS could delay the processing of your return, slow down any tax refund or disallow a tax credit if you don't have the identification numbers to support it.