When TurboTax asked whether the loan is secured by a property of yours, did you answer Yes? If the loan is not secured by a home that you own, the interest is not deductible. A mortgage loan is normally secured by the home that the loan was used to purchase. Answering this question incorrectly is probably the most common reason that mortgage interest is omitted from Schedule A.
If that's not the problem, go through the mortgage interest section of the interview again and check your other answers. If you are using the desktop TurboTax software make sure your software is updated.
