Mad as a hatter is a colloquial English phrase suggesting insanity.

Mad as a hatter may also refer to:

"Mad as a Hatter", an episode of Batman: The Animated Series "Mad as a Hatter", an episode of The Real Housewives of Dallas (season 1) "Mad as a Hatter", an episode of Ladies of London Mad As A Hatter (EP), by Def Wish Cast, 1993, and a track on the EP Mad as a Hatter, an album by Shadowland, 1996 "Mad as a hatter", part of mnemonic for features of anticholinergic syndrome

See also Mad Hatter (disambiguation) Hatter (disambiguation) Erethism, or mad hatter disease Mad as a March hare