I read My Sister's Keeper and I saw the movie (after I read the book). They changed the ending in the movie (Jodi Picoult used to have a statement on her website that once she sold the rights to the book she had no control over what they did in the movie, it might still be there I haven't looked). I don't know that I'd go so far as to say the movie was a disappointment -- it's still a good movie -- but you just need to be aware that unlike some movies I've seen where I've read the book and they followed the book pretty closely, this one had a very different ending. And as usual -- the book was better!!
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Ann