I am on an F1 visa since 2001 (a resident for tax purposes, hence). I married in 04 and my wife came here in 2004 (my wife is not working and is on an F2 dependent visa).

We have been filing resident tax returns since 2006 (1040).
In the W4 form, regarding marital status, it asks to put in single if spouse is non resident alien.
In my case, since we file joint resident taxes, I should select the "married" column, correct?

Thanks for your clarification.

Can anyone tell me whether my interpretation is correct?

Thanks.

You spouse is resident for tax purpose so you choose married.

Read Your U.S. Tax Return: Filing W4 Employee's Withholding Allowance Certificate

Agreed.

Note about your 2004 and 2005 tax return: you filed INCORRECTLY. You should have filed as a non-resident alien in those years. That IS something you should fix.

Thanks for the replies. What I meant is we filed 1040NR through 2005; from 2006 we filed 1040... sorry for that confusion.

In 2006 when we filed as residents, we did not send any letter explicitly informing that my wife was a NR, but chooses to be taxed as a resident. We assumed that by filing 1040, that becomes obvious. Were we supposed to write anything else?

Thanks.

The letter of the law says that the statement is required, but if you did not provide the statement, do not be concerned, because filing jointly DOES imply that fact.