Even though the employer is required to report in box 12 with code DD the cost of the employer-sponsored health insurance, since this is not a cafeteria plan the employer should not have excluded either the amount you paid or the amount they paid from the totals in boxes 1, 3 and 5. You should verify with your employer or against your wage statements [Edit: apparently you already did this] that this is indeed the case to confirm that you should be claiming the entire amount as a medical-expense deduction on Schedule A (assuming that your itemized deductions exceed the standard deduction). (If the employer had mistakenly excluded the amount from boxes 1, 3 and 5, they should really correct the W-2.)
