The Mystery of Mr. X
- Ano: 1934
- País: United States of America
- Xénero: Comedy, Crime, Mystery
- Estudo: Metro-Goldwyn-Mayer
- Palabra clave: diamond, jewel thief, pre-code
- Director: Edgar Selwyn
- Reparto: Robert Montgomery, Elizabeth Allan, Lewis Stone, Ralph Forbes, Henry Stephenson, Forrester Harvey