The man speaking on the radio in the room where Thornhill is being detained is Norm Heffron, a Rapid City radio-TV reporter on KOTA AM 1380 and KOTA TV channel 3.
The New York Central 20th Century Limited railcar featured (number 10006) was built by Pullman-Standard in 1939 and was scrapped in 1968. It was named "Imperial State" and featured four double bedrooms, four single compartments and two drawing rooms. The interior of the car seen in the film is actually a set built by MGM studios. When Cary Grant shuts the door, the wall can clearly be seen to move since the whole thing was manufactured out of plywood panels and painted to simulate the look of metal (including small fake rivets).
The song that's playing in the lobby of the hotel before Thornhill enters the Oak Bar is "It's a Most Unusual Day".
The studio wanted Sophia Loren for the female lead, and she wanted to do it, but contractual problems resulted in her having to turn it down. The part was eventually given to Eva Marie Saint.
The train station scene was shot in New York City's Grand Central Terminal. Among the onlookers watching the scene being filmed were future directors George A. Romero and Larry Cohen.
The two actors who played the Chicago auctioneer and his assistant, Les Tremayne and Olan Soule, succeeded each other as the lead on the popular radio show "Mr. First Nighter," during the 1930s and 1940s.
This film is the only one directed by Alfred Hitchcock that was released by MGM. However, MGM is now owned by Turner Entertainment - since 1996 a division of Warner Bros. - which owns the pre-1986 MGM library.
Thornhill appears on the left side of the screen for almost the entire movie.
When Martin Landau first sees Cary Grant, he says, "He's a well-tailored one." All of Landau's suits for the film were made by Grant's personal tailor.
While filming Vertigo, Alfred Hitchcock described some of the plot of this project to frequent Hitchcock leading man and "Vertigo" star James Stewart, who naturally assumed that Hitchcock meant to cast him in the Roger Thornhill role, and was eager to play it. Actually, Hitchcock wanted Cary Grant to play the role. By the time Hitchcock realized the misunderstanding, Stewart was so anxious to play Thornhill that rejecting him would have caused a great deal of disappointment. So Hitchcock delayed production on this film until Stewart was already safely committed to filming Otto Preminger's Anatomy of a Murder before "officially" offering him the North by Northwest role. Stewart had no choice; he had to turn down the offer, allowing Hitchcock to cast Grant, the actor he had wanted all along.
While on location at Mt. Rushmore, Eva Marie Saint discovered that Cary Grant would charge fans 15 cents for an autograph.