Originally, the Imagine Spot of the Girl bathing went on to show the plumber dropping his wrench into the tub. As he reaches into the suds for it, the Girl doesn't seem to mind him invading her space.
This dialogue the Girl delivers to Richard after having her skirt blown by the subway also never made it to theaters:
The Girl: This one's even cooler! Must be an express. Don't you wish you had a skirt? I feel so sorry for you in those hot pants.
A scene written, but probably never filmed, involved Richard's housekeeper finding a hairpin on his pillow, implying that he and the Girl slept together.
Executive Meddling: The act of adultery (consummated in the play) was removed by the censors, as were a few profanities and a few other bits considered risqué in 1955.
Fake Nationality: There's a whole tribe of fake Manhattan Indians at the beginning (as a narrator explains the anthropological origins of adultery).
Follow the Leader: At the time, very few movies opened with Artistic Title sequences. Saul Bass supplied the zany credits sequence here, and its success with audiences pretty much made his career. And in the 1960s and '70s, it seemed like every movie comedy opened with a cartoonish sequence of some sort, as did some Spaghetti Westerns.
The Pete Best: Vanessa Brown played The Girl in the stage version alongside Ewell, but was apparently not asked to reprise the role for the movie. (Then again, Ewell was almost not asked to reprise his role; see What Could Have Been below.)
Unintentional Period Piece: The film is a time capsule of the mid-1950s due to Values Dissonance and other reasons. For starters, the entire plot is set in motion when the wives and children of New York City leave for New England to escape the summer heat, which would not be necessary just a few years later when air-conditioning became more prevalent and reliable. The female characters, almost without exception, are seen wearing the high-waisted, long-skirted "New Look" style of dress that was already starting to pass out of fashion when this movie was made. The script is littered with subtle and not-so-subtle references to the popular culture of the time period, some of them bordering on (and in one case even crossing) the Celebrity Paradox: the characters going to a theater to see Creature from the Black Lagoon, a pretty blatant parody of From Here to Eternity, etc. Perhaps most striking, however, is the characters' discussion of the Marilyn character wearing nothing but a bikini for a U.S. Camera photo shoot: we are told that police had to show up on the beach to keep the crowd under control, and until we actually see the photo, the way the characters refer to it leads us to believe that The Girl had actually been posing nude.
Wag the Director: The Seven Year Itch was meant to be shot in black and white, but Marilyn's contract stated that all her movies should be shot in colour.