Factor X (disambiguation)

Factor X, also known as Stuart-Prower factor or as thrombokinase, is an enzyme.

Factor X may also refer to:
 * Factor X (Ailyn album), a 2007 album by Ailyn
 * Factor X (Chile), the Chilean version of The X Factor
 * Factor X (Portuguese TV series), the Portuguese version of The X Factor
 * Factor X (Spain), the Spanish version of The X Factor
 * El Factor X, the Colombian version of The X Factor
 * Factor X, a reference to protoporphyrin IX or haemin when used to identify Haemophilus influenzae in a microbiology laboratory
 * Factor X (hemin), found in chocolate agar
 * Serial killer Dennis Rader referred to his own lust for murder as “Factor X”