R

I am one of the many people that thinks this movie should be Pg-13, including the director, as you'll see if you look at the news article section, but i have to assume the reason for the rating is the violence. Though it was much worse in movies like jurassic park, the main shooting and the beating later, are pretty graphic, and while i don't think it's bad enough to be R, that must've been what the mpaa was thinking
they said it was for "some violence"

Brian de Palmas movies generally get R ratings. After all the MPAA stuff with Scarface and even Carlito's Way I think that they had made up their minds going in that they were giving the movie an R rating. Then they see it and can Definitley make a case for the movies rating. Violence and language were nowhere near the other two aforementioned movies but I guess it did not matter.