In the dance party scene where the layer cake falls off the beak of the totem pole and drops onto Miss Inch's face, writer and director David Swift originally wanted to cut the shot of the cake fall. But when producer Walt Disney saw the rushes, he told Swift to leave the shot in, saying it would be the biggest laugh in the movie. Disney was right.
The screenplay originally called for only a few trick photography shots of Hayley Mills in scenes with herself. The bulk of the movie was to be shot using a body double. When producer Walt Disney saw how seamless the processed shots were, he ordered the script reconfigured to include more of the visual effect.
For the scene where Maggie McKendrick (Maureen O'Hara) and Charles McKendrick (Charles Ruggles) are speaking in the bedroom, Ruggles didn't have any place to put the ashes of his cigarette. Writer and director David Swift mentioned someone he knew who put the ashes in his hand, and Ruggles asked for permission to use this. He did this in so casual a way that the ashes would be on the floor a few seconds later.
Joanna Barnes (Vicky Robinson) is the only actress to also appear in The Parent Trap (1998). She plays an older version of her character, who has passed her gold digging ways on to her daughter Meredith.
In the shot where Mitch Evers trips on the chair, Brian Keith fell so hard he cracked a rib and kept right on with the scene.