The fourth Harry Potter film, the Goblet of Fire, has been given an older 12A rating in the UK because it is "scarier and darker" than the others.
Staff at the British Board of Film Classification told CBBC Newsround that this film is more frightening than the first three movies.
The other Harry Potter films have all been given a PG rating.
The 12A rating means that under 12s can go and see it but only if they are with a parent or guardian.
A spokeswoman for the British Board of Film Classification, which decides on the age ratings for all movies, said viewers should be "prepared for a very different film to the first three".
She went on: "Examiners decided that the 12A was the most suitable category, as younger or more sensitive viewers could be frightened by some of the more intense scenes (which I can't reveal as you'd get upset with me!).
A dragon from the trailer
"The ending was a shock too, although maybe if you have read the books, you'll be expecting it anyway. At 12A, we allow moderate level violence, but without focus on injuries or blood."
The spokeswoman added that no scenes had been cut from the Goblet of Fire, it had just been given a slightly older rating to allow for some of the darker scenes.
Goblet of Fire was given a PG-13 rating in the US.