I mailed my tax return and check but forgot to include the 1099's. What do I do?

You only need to include forms that show federal withholding with your return.  If you forgot to include those forms when you mailed your return, the IRS will probably send you a notice.  This notice is nothing to panic over though.  The IRS should be requesting the copies of the forms with federal withholding on them.  Simply respond to the letter and attach the forms that are requested.

You do have the option of mailing a second copy of your return with the 1099's and a cover page stating this is a resubmitted tax return because you forgot to attach the 1099's.  Due to processing times you may still get an IRS notice requesting the forms though.

Do not send the forms to the IRS without a return or the notice from the IRS.  If you do the IRS will not know why you sent the forms and will not apply them to your account correctly.