I am separated form my husband and do not know his social security number

In order to e-file your return you will need his social security number. You can print/mail your married filing separate return without his social security number.  Follow the filing prompts to print/mail your return in the "Filing" section of your interview.

The best option may still be to find/obtain his social security number.  Maybe you can find it on a previously filed return.  Also, he will need your social security number to file his separate return so he could possibly contact you.  

Another option that may be available to you is in certain circumstances you may be considered unmarried for the year or be able to file head of household and not need his social. 

Unmarried persons.

You are considered unmarried for the whole year if, on the last day of your tax year, you are either:

Unmarried, or Legally separated from your spouse under a divorce or separate maintenance decree.

State law governs whether you are married or legally separated under a divorce or separate maintenance decree.   

You may also be considered Unmarried and file head of household if:

1. You file a separate return

2. You paid more than half the cost of keeping up your home for the tax year.

3. Your spouse did not live in your home during the last 6 months of the tax year. Your

spouse is considered to live in your home even if he or she is temporarily absent due to special circumstances.

4. Your home was the main home of your child, stepchild, or foster child for more than half the year.

5. You must be able to claim an exemption for the child.