I'm an italian citizen working in USA as a self employed and paid by an european company. I've been working more than 183 days during 2009, I have a B1 visa and I'm not resident in USA. Should I pay taxes in USA?

Thanks for your help.

From IRS Publication 901
"Income that residents of Italy receive for performing personal services in the United States during the tax year as independent contractors or self-employed individuals (independent personal services) is exempt from U.S. income tax if the residents:
* Are present in the United States for no more than 183 days in the tax year, and
* Do not have a fixed base regularly available to them in the United States for performing the services.
* If they have a fixed base available, they are taxed only on the income attributable to the fixed base."

Based on your posting, your self-employment income IS subject to U.S. income taxes because you have exceeded 183 days in the U.S.

For sure, you can file a dual-status return. You MAY be able to file jointly with your spouse (if you are married) and file as resident aliens under First Year Choice. It will require that you claim ALL world-wide income for both you and your spouse, but you can claim the Foreign Tax Credit (Form 1116) to offset any double taxation.

STRONGLY suggest you get professional tax help, as the return in question will be rather complex regardless of how you file.