Hostility on the Set: Ron Moody noted that several members of the original West End stage cast (1960) did not get along saying: "It was not a happy company". He personally had a poor relationship with Georgia Brown, who was the original Nancy. When the film came to be made, Brown blamed Moody for her not being cast as Nancy. However, Moody categorically denied this, saying he had no say or influence whatsoever over the casting of the film and he himself was far from first choice to play Fagin despite his success on stage.
Michael Caine auditioned for the part of Bill Sikes in the original show.
Sid James was offered the part of Fagin, but turned it down as he wanted to avoid being typecast as criminal types.
Actor-Inspired Element: When Nancy asks Bill if he loves her and Bill says, "Of course I do, I live with you, don't I?" Oliver Reed came up with this - he was walking through a very tough neighborhood one day and heard a woman saying, "Don't you love me" and a man saying, "Of course I do, I fucks you, don't I" Reed wanted to use it in the movie, but director Carol Reed wouldn't let him, so they used it, but changed it to "live with".
Cross-Dressing Voices: Mark Lester's singing voice wasn't up to snuff, so his singing was dubbed by Kathe Green, whose father Johnny was the film's music arranger. It makes for very eerie watching.
The film omits "I Shall Scream", one of the songs sung by Mr. Bumble and the widow Corney (whose roles are larger in the stage version than in the film). It also omits nearly all of the reprises of the show's other songs, with the exception of the songs "Who Will Buy?" and the comical "Reviewing the Situation", giving the second half of the film a more serious, gloomy quality than Act II of the stage production.
Sikes' song "My Name" was cut. Officially because the producers decided that Bill Sikes should not sing, but also allegedly because there was concern over the quality of Oliver Reed's singing voice. However, the instrumental version is played in the background when the audience is first introduced to Bill Sikes.
Dawson Casting: Although many viewers assumed Jack Wild was one of the youngest members of Fagin's gang, he was actually the second oldest. He celebrated his 15th birthday during filming.
Deleted Role: Studio Records list Veronica Page as Oliver's Mother and Henry Kay as the Doctor attending to Oliver's birth, but these performers were not seen in the movie. It is not known if they were not filmed or filmed and not used.
While filming the scene where Oliver gets a peek at Fagin's treasure, director Carol Reed was not satisfied with the reaction on Mark Lester's face. Later, while re-shooting the scene, he hid a small white rabbit in his pocket and stood behind the camera. As Ron Moody opened the box of treasures, Reed pulled the rabbit out of his pocket. Lester's reaction to the sight of the rabbit was then used in the final film.
Oliver Reed always appeared in full costume and makeup before the children in the cast and maintained a distance from them during filming; Mark Lester later reported that all of the kids were legitimately terrified of him. He lightened up after filming was complete. (The dog playing Bullseye liked him so much that, late in the story when the dog is supposed to have turned on him, they had to tape the dog's tail to his leg to keep it from wagging whenever he saw Reed.)