In the scene where Alex approaches the two girls at the record stand you can see the original score for 2001: A Space Odyssey.

The scene where Alex has sex with the two girls in fast forward wasn't done as an artistic statement, Kubrick just sped the scene up so he could get it past the censors and the MPAA.

In the scene where Alex and his Droogs break into the writer's house, Alex starts to sing 'Singing in the Rain'. This came about after Stanley Kubrick asked Malcolm McDowell whether he could sing during the scene; Malcolm chose that song as it was the only song he knew the words to, start to finish.

The book that F. Alexander is writing when the droogs burst in and attack his wife is "A Clockwork Orange."

During the filming of the Ludovico scene, Malcolm McDowell actually had one of his corneas scratched. He states that he didn't realize it until he was leaving the set that night and the anesthetic wore off. He also states that it felt like someone hammered a nail into his eye.

The movie is actually not the entire story of the book. The US release was published without the final chapter because Burgess' New York publisher thought it was a kill joy and believed US audiences wouldn't like it. Despite the fact that the directer was English, he decided to write the movie based on the US version, thus leaving out the final chapter.

Stanley Kubrick introduced Basil, Alex's pet snake, only after he discovered that Malcolm MacDowell is terrified of snakes in real life.