Kitty Carlisle initially refused to take the part when she was asked to mime to someone else's voice. She won, and the song she performs, "Alone", later became her signature tune.

Kitty Carlisle stated that, out of her decades of movie roles, co-starring with The Marx Brothers in this movie gained her the most recognition.

Sam Wood, freshman The Marx Brothers director in this film, was a perfectionist. The scene in which Harpo Marx hangs from the rope was filmed so many times that Harpo Marx's hands became cut and swollen from the rope.

Sig Ruman makes his first of three appearances in The Marx Brothers films.

Harpo Marx did many of his own stunts. He later said it was a silly thing for a 47-year-old non-stuntman to have done.

A persistent rumor involves the presence of The Marx Brothers' father, Sam Marx (aka "Frenchie"), in the film as the ship leaves dock. He is not in this film - he died in 1933. The rumor came about because he had a cameo in a similar scene in Monkey Business.

According to MGM's dialogue cutting continuity, the film originally began (after the opening credits) with the image of a "boat on canal." A superimposed title reads: "ITALY - WHERE THEY SING ALL DAY AND GO TO THE OPERA AT NIGHT." What follows is a musical number featuring bits and pieces from Ruggero Leoncavallo's "Pagliacci" performed by "everyday" Italians. A street sweeper sings part of the prologue ("Un nido di memorie...") as he greets a man who then hands out opera tickets to a group of children emerging from a store; the kids respond with "la-la-la-la-la, verso un paese strano." A "captain" comes down a set of steps, salutes a sentry, then bursts into "Vesti la giubba." There's a lap dissolve to a hotel lobby, where a "baggage man" is rolling a trunk and crooning about "nettare divino" (divine nectar). He's joined in song by a waiter who then enters the dining room, where he sings as he serves a man who also gets in a few notes. The waiter then crosses over to speak to Mrs. Claypool (Margaret Dumont), marking the beginning of the film in existing copies.

An additional scene was cut from the picture in subsequent releases, and is now considered lost. The scene occurred just after the scene in the park when Rosa tells her friends she has been fired from the opera. The Marx Brothers, Rosa, and Ricardo hop on a passing fire engine, which takes them to the opera house. After lighting his cigar in the fire engine's smokestack, Groucho Marx comments, "This is the first car I've ever been in where the cigarette lighter actually works!"

Groucho does a very brief Jack Benny impression in the film. After "Otis P. Driftwood" makes the speech to the audience, Groucho gestures to the orchestra pit and says, "Play, Don!" This is a Benny line from the radio series; Jack Benny's orchestra leader, Don Bestor, was always cued this way (by the way, Bestor originated the J-e-l-l-O jingle for the Benny show).

In Leonard Maltin's commentary on the current DVD release, he states that there was a longer opening sequence. Starting with a title card that places the movie in Milan, Italy, there was then a musical number in which people on the street were "passing along" the melody line of a song, as in the Maurice Chevalier vehicle Love Me Tonight. The song was followed into the restaurant where Mrs. Claypool was waiting for Otis B. Driftwood. Maltin says the scene was cut during World War II to remove references to Italy, and unfortunately, the main negative was cut as well, so the scene is now lost. This was why the stated running time of the movie was three minutes longer than it is now.

In 2007, the American Film Institute ranked this as the #85 Greatest American Movie of All Time. It was the first inclusion of this film on the list.

In exasperation after several attempts to have Groucho Marx read one of his lines in the manner director Sam Wood had requested, Wood exclaimed, "I guess you just can't make an actor out of clay." Groucho Marx instantly responded, "Nor a director out of Wood."

In the scene where Harpo Marx, Chico Marx and Allan Jones are impersonating the three aviators in front of the mayor, Groucho Marx turns around to speak to them in a "foreign language." What is actually being said is a direct response to the accusations of imposters, only the audio track is played backwards. The first time Groucho Marx actually says, "Did you hear what he said? He said you were frauds and imposters!" which is then followed by Chico Marx and Riccardo protesting loudly, "How can he say a thing like that?", "This is ridiculous," and other such comments.

Premiere voted this movie as one of "The 50 Greatest Comedies Of All Time" in 2006.

Producer Irving Thalberg would often call people in for meetings, and then keep them waiting in his office for hours while he attended other meetings on the MGM lot. One day, during pre-production for A Night at the Opera, Thalberg kept The Marx Brothers waiting for several hours in his secretary's office, while he was in his own office making phone calls. When Thalberg's secretary went home for the day, the brothers decided they'd had enough. They pushed the office file cabinets against Thalberg's door, trapping the producer in his office. Afterwards, Thalberg kept his appointments with the Marx Brothers, but would often interrupt his meetings with them and step out to attend other meetings - again keeping the brothers waiting for hours. One day, Thalberg came back from another meeting to find Groucho Marx, Chico Marx, and Harpo Marx sitting in his office completely naked, and roasting potatoes on sticks in his office fireplace. Thalberg sat down with them, had a potato, and never missed or interrupted another meeting with the Marx Brothers.

The famous "stateroom scene" was originally conceived as a way of getting a cheap laugh by having Groucho Marx, crowded out of his room, changing his pants in the corridor. After this was not liked by test audiences, the current scene was improvised on the spot. A total of 15 people were in the scene:
  • Driftwood (1)
  • the stowaways Fiorello, Tomasso and Riccardo who were in the trunk (2-4)
  • two chambermaids (5-6)
  • an engineer who comes to turn off the heat (7)
  • a manicurist (8)
  • the engineer's burly assistant (9)
  • a young woman looking for her Aunt Minnie and asking to use the phone (10)
  • a cleaning woman (11)
  • and four staff stewards bearing trays of food (12-15).
  • They all tumble out when Mrs. Claypool (Margaret Dumont) opens the door.

The film was to have originally begun with each of The Marx Brothers taking turns roaring in lieu of Leo the Lion (MGM's logo mascot); Harpo Marx was to have honked his horn.

The first Marx Brothers film made without brother Zeppo Marx, it started a new trend of The Marx Brothers movies featuring a Zeppo-like supporting character who carries the love story and sings the song.

The first storyline was about Groucho Marx as the producer of an opera. That story was dropped but appeared many times in Hollywood as a story idea - until Mel Brooks made The Producers and got an Academy Award.

The opera performed as the movie's climax is Giuseppe Verdi's Il Trovatore.