You can only petition for your parents if you are a US citizen AND if your parents entered the US lawfully. If they did not, they will not be eligible to adjust status within the US but would have to consular process in their home country. However, if they entered lawfully but have since overstayed, then you can petition for them and they will be able to adjust status within the US.
Answered on Dec 08th, 2011 at 9:34 PM