CM says no, it was all too much Hollywood. He linked this, from Wiki. Which claims the "possession" was all just the delusions of a mentally ill girl.
Jacafamala, forgive me, my intent was not to state I disbelieve the possession, but that the name of the girl was not Emily Rose, but Annelise Michelle. I believe that she was possessed as well, but that the spin Hollywood put on the story was malarkey.
I didn't read the Wikipedia article, rather I just linked to the first Google hit that had the correct name. The Dimonds actually have an audio on her that is worth listening to.
Sorry for the confusion.