What drew John C. Reilly to play Larten Crepsley was "the fact that it was a real person, that he wasn't some supernatural mystical being that can turn into a vampire bat. The powers weren't so extreme that it was just another thing altogether, that this guy was a person who was alive in the 1800s who was essentially about my age. If you account the slow aging, he is forty something years old" he said.
The movie Cirque du freak is based on a book series, written by Darren Shan. It consists of twelve books, but the movie only covers three.
The character of Mr. Tall played by Ken Watanabe is an homage to Zhan Shichai (stage name "Chang Woo Gow") who was a Chinese man who toured the world as "Chang the Chinese Giant" in a 19th century sideshow with P.T. Barnum. His height was claimed to be over 8 feet (2.44 m).
The extras in the school scenes were actual students of the school where this was filmed.
A portion of the film was shot in Studio 28 at Universal Studios in Los Angeles. It is the oldest sound stage still in use at the studio.