It is important to provide documentation about your retirement accounts or 401K programs because this is another asset you could draw upon as reserves in case of a problem. It is also another way to show you have a savings history. Just provide a copy of your most recent statement to your lender.
Many people use these accounts as a source of funds for their down payment, too. Some employers allow you to "cash out" a portion of the 401K and some allow you to borrow against it. Be sure to keep copies of all paperwork involving the transaction. If they cut you a check, be sure to make a photocopy of that, too, including any receipt for deposit into your personal bank account.
