In the scene when Cary Grant is going up the steps to the UN, Alfred Hitchcock shot it from a rug truck across the street. He wasn't allowed to shoot the front of the UN. If you look closly, you can see a security guard in the left corner.

After Eva Marie Saint snatches the sculpture containing the microfilm from James Mason, Cary Grant remarks, "I see you got the pumpkin." This was evidently a reference to the Alger Hiss case, in which Whitaker Chambers testified that Hiss had given him government secrets that had been hidden in a scooped out pumpkin in a pumpkin patch in Hiss' back yard.

Cary Grant was born on January 18th, 1904, and the actress playing his mother, Jessie Royce Landis, was born on November 25th, 1896, making her just seven years older than Cary. According to commentary on the DVD, it was thought that casting Landis as Cary Grant's mother would make Cary look young enough to be a believable love interest for Eva Marie Saint.

In the auction gallery, Cary Grant says to Eva Marie Saint, whom he sees with the spies for the first time, "The three of you together: here's a picture only Charles Addams could draw." This referred to a New Yorker cartoonist who specialized in macabre and grotesque characters. The reference would probably have been lost to Italian viewers, but the dubber did his homework, and the translation was, "The three of you together: just like something out of Dracula and Frankenstein."

Alfred Hitchcock's Cameo comes at the end of the opening credits, he can be found missing the bus.