According to the filmmaker's commentary on the DVD version of this film, because of the loud noise from the sea and jungle on the beaches of the islands on which the movie was set, none of the dialogue could be recorded on the actual locations where the scenes were filmed. Instead, at the end of each day, the actors would be taken to a quiet location in the interior of the islands, where the dialogue for the scenes they had just filmed would be recorded and re-dubbed during the editing process. The one exception is the scene where Piggy tells some of the younger children how his hometown of Camberly got its name (which is also the only scene in the movie which is not based on a scene in the original book.)
Director Peter Brook saw over 3000 boy actors before choosing his cast.
During the first week of film shooting on the Island of Vieques, Puerto Rico, the Bay of Pigs Invasion began. This impacted filming because the wounded were evacuated to the U.S. naval hospital on Vieques.
Eleven-year-old Hugh Edwards, who plays Piggy in the film, landed his role by writing a letter to the director which read, "Dear Sir, I am fat and wear spectacles."
In 1996, 35 years after the film was made, the BBC created a documentary about the making of the film called "Time Flies", which reunited the main cast and crew on the beaches of the Caribbean where it was filmed; an article written by one of the actors, Tom Gaman, mentioned that of the boys, only the one who played Ralph (James Aubrey), pursued an acting career. Others went on to have very different ones: Gaman became a freelance forester in Inverness, California; Hugh Edwards (Piggy) became an engineer for a Russian firm; Tom Chapin became a gold mine geologist in Nevada and the twins David Surtees and Simon Surtees (Samaneric) remained together, living with their families in the UK and working as a guidance counselor and political administrator respectively. (NOTE: Contrary to Mr. Gaman's article, another of the boys besides James Aubrey, Nicholas Hammond, who played Robert, had a quite extensive film AND TV career, playing, among other roles, one of the children in The Sound o
Once filming began, Peter Brook largely dispensed with the script and encouraged his young cast to improvise. He shot over 60 hours of footage which was then edited down into a 90-minute film. Consequently, there is no screenplay credit.
The 60 hours of film from the 1961 shoot was edited down to 4 hours, according to editor Gerald Feil. This was further edited down to a 100-minute feature that was shown at the 1963 Cannes Film Festival (May 9 to 22), but the cuts necessitated that new audio transitions and some dialog changes be dubbed into the film more than a year after shooting. The voice of James Aubrey, who played Ralph, had dropped three octaves and was electronically manipulated to better approximate his earlier voice, but it is still significantly different. Tom Chapin, who played Jack, had lost his English accent and another boy's voice was used to dub his parts. The U.S. distributor insisted the film be further edited to 90 minutes, so one fire scene and scenes developing the character Ralph were cut.