Yes, you should keep your old tax returns for at least 7 years. When a return contains information pertaining to the basis of property owned, it should be kept until that property is sold. One of the benefits of keeping your tax returns from year to year is that you can look at last years return while preparing this years. If you do throw out an old return you may fill out form 4506, Request for Copy or Transcript of Tax Form, and send it to the IRS service center where you filed your return.