It, of course, depends on which movie you mean, but I'm assuming you mean the 1931 classic.
- In the movie the monster never speaks. In the book he has a lot to say.
- In the movie the monster is burned to death. In the book he leaves 'for the farthest shore.'
- In the movie Frankenstein's assistant, Fritz (aka Igor), gets an abnormal brian. In the book there is no Igor and no problem with the brain.
- In the book the doctor's younger brother is killed. In the movie there is no younger brother, only Frankenstein's father the Baron.
- In the book, Frankenstein's first name was Victor and his friend's name was Henry. In the movie their names are reversed.
