I can imagine that for many people this is the one film they have watched about Anne Frank and her diary, but although this film is very popular there are many flaws with it and it is not that faithful to Anne's life.
For me Millie Perkins is almost nothing like Anne. Fair enough she does capture Anne's sillyness and sense of fun in parts of the film but for the rest she just appears to act like a 1950s American teenager rather than the German/Dutch girl brought up in the 30s and 40s which Anne Frank was. Anne's relationship with Peter I think was over exaggerated. In the film it shows them together to the end, Anne and Peter kissing in the annex attic waiting for the Gestapo to take them away. However, in reality this romantic relationship had broken down a few months before and although they still liked each other, Anne didn't have those feelings for Peter anymore.
As this film was based on the play (which was based on the diary) it gives a very unflattering portrayal of Fritz Pfeffer (called Albert Dussel in the film and play). In the film Dussel comes across as a comic interlude, a character with no real backbone (possibly with the exception of when he is telling those in hiding about the deportations). I can imagine that he was much more dignified and intellegent in real life.
The way this film portrays the arrest of those in hiding also deviates greatly from what actually happened. However, I can imagine these changes were brought in for dramatic affect (The Frank family never knew they were going to be arrested on 4th August 1944, nor did they hear a telephone ring!).
Despite all its flaws, "The Diary of Anne Frank" is good in the way it uses location shooting. It has outdoor shots of the actual building where the family hid as well as the sound of the Westerkerk bells nearby.
Overall "The Diary of Anne Frank" is a good Hollywood film, but if you are wanting to find out about Anne Frank's life, I'd suggest you'd look up the film Anne Frank: The Whole Story
before renting this film.