Romans 2:12-15 (NKJV)
For as many as have sinned without law will also perish without law, and as many as have sinned in the law will be judged by the law (for not the hearers of the law are just in the sight of God, but the doers of the law will be justified; for when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves, who show the work of the law written in their hearts, their conscience also bearing witness, and between themselves their thoughts accusing or else excusing them)
This question gets asked a lot: "What about those who have never heard the Gospel, wouldn't it be unfair for God to condemn them?" This is a hard question and many things about the question bother me.
One thing that bothers me about this question is that its premise assumes that God judges man on the basis of whether he accepts or rejects Christ. No matter how solid the logic is, if it is based on faulty assumptions it will lead to a faulty conclusion. This verse may shed some light on this issue. Every man has a conscience and who can say they have always obeyed their conscience? Men are judged on the basis of what they know to be right. Rejecting Christ does not make a man guilty; he is already guilty even before he has a chance to accept Christ.
Another thing that bothers me is that it suggests that God might be unfair. Unfairness is not the picture the Bible paints of God, rather the Bible tells us of a loving, perfectly just, merciful God, slow to anger and longsuffering toward us. Someone made the point that we don't want fair, what we really need is mercy. That is indeed what God offers as a free gift through Jesus Christ.