During production, Liam Aiken grew four and a half inches (11.4 centimeters), requiring adjustments to his costume throughout. By the end of the movie, he is visibly taller than Emily Browning, who portrayed his older sister.
When the children first meet Count Olaf and Jim Carrey says, "Wait, let me do that one more time. Give me the line again, quickly, while its fresh in my mind." was not actually in the script. Carrey accidentally forgot his line and staying in character, wanting to try it again, but they kept the cameras rolling and felt it worked the way it happened.
After scouring ballet schools looking for a girl to play Violet Baudelaire, casting director Avy Kaufman was exercising at the gym when she spotted Emily Browning on television, and decided to get her for an audition.
Tim Burton was attached to direct at some point, with Johnny Depp playing Count Olaf and Glenn Close playing Aunt Josephine. When Burton left the project, Depp left as well. Brad Silberling replaced Close, feeling that Meryl Streep would be better for the role. Streep accepted the role of Aunt Josephine upon the request of her daughter, a huge fan of the books.