If he entered the US unlawfully, under the current immigration laws he will not be able to adjust status to permanent residence within the US but will have to go back to his home country. However, as soon as he departs the US, he will trigger an automatic 10 year bar to reentry, which can only be waived by a showing of extreme hardship to a US citizen spouse, which is fairly difficult to do in most cases.
Answered on Mar 06th, 2013 at 1:56 PM