Alison Lohman went to the audition dressed and acted like a 14-year-old girl. Ridley Scott only realized her real age when she told him. She was 23 at the time.
Roy's pills are actually Benadryl, a popular over-the-counter allergy medicine.
At one point, in its development stages before Ridley Scott was hired, Steven Spielberg was asked to direct, but he turned down so he could direct Prova a prendermi (2002) instead.
Frank Mercer was named for Frank Sinatra and Johnny Mercer. Roy Waller is seen playing records by the two.
The airport scenes, set at Los Angeles International Airport (LAX), were actually filmed in the main entrance of the Anaheim Convention Center, a mile south of Disneyland. Due to changed security measures in the nation's airports, filming rights have been severely restricted on airport property.