Originally Posted by
ralfp
This is okay if you can enter the destination country with a US passport w/o a visa.
If you exit the US with a US passport (what does that mean?) then the airline might not let you on the aircraft to Brazil w/o a visa. If you exit with a Brazilian passport, then, well, I dunno...
Not necessarily. I traveled once with a dual citizen leaving JFK for Brazil who showed his US passport to the airline clerk, who noted there was no Brazilian visa. He then showed his European passport, which requires no visa for Brazil, and proceeded to Rio.