You are automatically a US citizen if born in the US, with the foreign diplomat exception noted. You might not do anything about it formally, but you still have the rights and obligations whether these are followed up or not.
http://www.nolo.com/article.cfm/Obje...8/209/286/ART/

...which better explains my question...someone is born in the US to british parents who leave soon after their birth. they are raised in britain. they never had a US PP or it is long since expired. they want to visit the US but they don't have a US PP. I think common sense would say that most people would just travel on their british pp and not worry about it but it seems to be a legal black hole.

Hi,
As a US citizen, you have to use your US passport to leave and enter the USA. In Europe and elsewhere you can use either but it makes sense to use the EU passport within the EU. My children are dual passport holders, I have a UK passport and green card.
Carolina

This thread was pulled up as I research possible dual citizenship with Italy.

Just wanted to state that carrying two passports is not illegal. You're not breaking any laws, even if immigration or customs officials act differently.