- Acting for Two: Karl Swenson played "Doc Isdell" and the bartender in the scene where Tom auctioned his eye.
- The Danza: John Wayne as John Elder.
- Dawson Casting: John Wayne was 57 when he played John Elder, a man who is supposed to be in his late thirties or early forties.
- Prop Recycling: The same wanted poster of a man in a top hat smoking a cigar was used in El Dorado - also starring John Wayne.
- Role-Ending Misdemeanor: Tommy Kirk was fired from the film after being arrested for possession of marijuana at a party on Christmas Eve 1964. Photographs of him wearing police handcuffs made the front pages of newspapers, and consequently he found it increasingly difficult to get film roles.
- Troubled Production: It is said that John Wayne was so unwell during production that he required an oxygen mask between takes.
- What Could Have Been: When it seemed unlikely that John Wayne would do the film because of his cancer, he suggested that Kirk Douglas replace him, while the producer suggested Robert Mitchum or William Holden.
Trivia / The Sons of Katie Elder