Is the amount that I contribute to my group health insurance (it says on pay stub that it is a pre-tax contribution) supposed to be deducted from my income in Box 1 of my W2? I see where my 401k contribution was deducted from my total income, but the amount I contributed to my health insurance is still included in box 1.

The taxable wages for federal income tax (box 1) do not have to match the taxable wages for Social Security (box 3), Medicare (box 5), or state income tax (box 17). There are legitimate circumstances in which these amounts should be different. An example of this situation is if you participate in Deferred Compensation such as 401k. Box 1 of Form W-2 is used to report the total federally taxable income earned during the year. If there is an error on your W-2, the ER can file an amended W-2. When the ER files for a correction, you will receive a W-2c, or corrected form for your correct return. If you have already filed your taxes before the error was discovered, you can still request an amended W-2. You will then need to file a Form 1040-X, or amended return, to reflect the changes. If you do not notify your employer of the error, you will be required to file and pay taxes based on the information contained on the erroneous form. If you do not notify your ER of the error, you will be required to file and pay taxes based on the information contained on the erroneous form.