I have a cousin where his father is a U.S. Citizen and filed a petition for his son back on August of 2000. His son was here in the United States at that time and he has enough evidence to prove that he was here on December 21, 2000. The USCIS approved this petition on May of 2003. My question is: whether my cousin can apply for the adjustment of status and the Employment authorization based on the 245(i) and his previous approved application or not? Thanks.

how old is your cousin?

Your cousin can apply for AOS and EAD based on 245(i) once the date of the petition becomes current (assuming she/he was over 21 when the petition was filed or when the father became USC, that will be in 5 - 17 years, depending if she/he is unmarried/married and from which country). http://travel.state.gov/visa/frvi/bulletin/bulletin_3925.html

When did your cousin's father become a U.S. Citizen?
He filed a petition for his son in August 2000,
What is the status of your cousin now?

Thanks Adam for your help.
My cousin's father became U.S. Citizen back on May of 2003 almost 3 years after the petition was filed.
My cousin's status is without inspection = illegal. He is single and no felonies.

Your cousin's situation is a straight forward 245(i) eligible case. Your cousin was petitioned by the father while still a permanent resident in 2000, but got naturalized in 2003. They have the option of either upgrading the I-130 to F-1 (unmarried son/daughter of USC) or opting-out to retain the F-2B (unmarried son/daughter of an LPR) priority date. But it depends on which of the two family preferences as per country of origin is more beneficial. They need to be guided by an immigration practitioner through the whole process.

Follow the instructions of Rough Neighbor.
F-1 is for unmarried son/daughter of U.S. Citizen
(F-2B, unmarried son/daughter of an LPR)
Your cousin's father can upgrade this Petitions(I-130)by calling National Customer Service
giving his detailed information as to when he had become a Citizen. Date, Place, Naturalization Certificate Number, His Alien # your cousin's name date of Birth, place of Birth and his file # on the left hand side of the Notice of Action which give an approval of his I-130.
Before he calls the NCS he should check on web page the processing dates for F-1 and F-2B.
To see which is faster F-1, or F-2B.
Country of origin is more important in all the cases.
My friend has taken the same action and his children are now LPR.
Wish you all the best.

Thanks Rough Neighbor for your advice and help. I have a final question: in your previous comment you said that my uncle could choose between F1 and F2B to proceed with the adjustment status for my cousin. How he can choose the option? I mean, by simply filing the I-485 or there is a certain and special procedure to choose the category for which the petition should be processed. Thanks again for the help.

As I said before, your uncle and cousin should be assisted by an immigration practitioner. Adam's recommended procedure above may be one option, by calling the 1-800... National Customer Service Center to upgrade the I-130 to F-1 or to opt-out to retain the F-2B priority date. But in my opinion, it's always better to "document" all steps one takes when dealing with the USCIS. The lawyer that they will hire should know where to write what.

I see this only now.

Yes, I think he would be able to file based on the I-130 that was filed in 2000. USCIS - by the way there is lots of information to be found in their published files on the website, just put in 245i into the search engine - only lookes at whether a petion has been filed. As long as he can proof that the petion has been filed prior to the cut-off date, he can piggy back on that petion.

I filed like that.

buena suerte ,con esa aplicacion.no creo que tenga ningun problema para que le aprueven su aplicacion.

creo tan también, pero sería beter si usted apenas escribe el tiempo próximo inglés porque no todos puede leer a españoles, le agradece

I am want to say thank you all for your advise and comments.

Javi: So long as your cousin has not left America since the initial application was filed, then he is eligible for 245i.

He will most likely encounter problems, however, if he has worked in the country without authorization.