At one point during the production, Liza Minnelli was supposed to board a bus in front of Bergdorf's on Fifth Avenue. When a real bus came along, she boarded it thinking it was the "movie bus". Not until she was halfway down the block did she realize her blunder when she looked back and saw the whole crew cracking up.

Dudley Moore was said to have based his performance partly on Peter Cook, whose excessive drinking had soured his and Moore's comedic partnership in the 1970s.

Dudley Moore kept cracking up the cast and crew, so much so that 27 takes were needed to get one scene filmed.

Apparently, writer and director Steve Gordon had originally wanted to cast George Segal in the lead role of Arthur. After the box-office success of 10 (1979), however, Dudley Moore replaced Segal. This movie was actually the second time that Moore replaced Segal. Segal was originally cast in the lead role in 10 (1979), but Segal apparently walked off the set shortly after filming began. Reportedly, this was rumored because Julie Andrews' role had been built up. Apparently, after 10 (1979) had been released, Segal, when once asked if he had seen the movie, allegedly replied with a finger gesture.

Sir John Gielgud turned down the role of Hobson several times, finally accepting it only because the salary he was offered was too good to pass up.

Continuity

The length of Arthur's hair changes back and forth throughout the final scenes.

At the engagement party, Linda leans over the gentleman's shoulder to get her cigarette lit. Seconds later, while stepping back to observe the party, she asks the same gentleman to light the same cigarette.

The position of Arthur's top hat changes in the bathtub scene after Hobson places it on the edge.

Arthur grabs his martini glass twice in the bathtub.

When Hobson comes to Linda's apartment, she comes out of her bedroom and closes the door behind her. Later in the scene, the door is open.



Incorrectly regarded as goofs

Linda steals the tie from Bergdorf-Goodman's by itself, yet when Arthur helps her into the Rolls-Royce, he hands her a box that contains the tie; she still has the box with her when Bitterman helps her out of the car. When Arthur and Hobson walk up to Linda during her confrontation with the security guard, Hobson is carrying a bag with a large box in it. That's the box Linda was given. Since it contains the tie she stole, presumably the tie was put in that box off-camera.

When Bitterman drops Linda off at her apartment complex, she looks out the back window of the car and asks that he wait until her neighbor is there before he opens the car door for her. When Linda does get out of the car, the woman is approaching the car from the front, not from the back. However, Linda was looking in all directions for any neighbor who might be approaching.



Revealing mistakes

At the wedding scene, all the expensive cars have license plates beginning with "Z". At that time in New York, only rented cars had license plates beginning with Z. It is clear that these cars were rented for the scene and are not actually owned by the churchgoers.

(at around 51 mins) Arthur is at Perry's door, while looking for Linda. Perry's wife opens the door and mouths some of Arthur's dialogue. She mouths the lines beginning with, "Very sorry to disturb you, Madam..." The last line she mouths is, "I hope this is the wrong house, no offense."



Audio/visual unsynchronized

During Arthur's engagement party, a live band is playing. At one point, a hi-hat is clearly heard while the drummer plays cymbals.



Character error

At the end of the shoplifting scene with Linda, Arthur, Hobson and the Bergdorf-Goodman security guard, as the crowd breaks up, a passerby inexplicably looks directly into the camera, smiles and gives the "okay" sign.

In Bergdoff's, after ordering two dozen green sweaters, Arthur tells Hobson he doesn't wear sweaters. However in the next scene, in the flower shop, he is wearing a purple sweater.