Atom Mizuishi was brought on as a motion-capture actor for Alphonse Elric. Director Fumihiko Sori was so impressed with his performance that he cast Mizuishi as Alphonse's voice actor too, with approval from Alphonse's original voice actor Rie Kugimiya.
Fumihiko Sori wanted the story to fit within one film, but as the "Fullmetal Alchemist" manga was very long (2001-2010) he decided to adapt about a third of the original source material.
The map used to locate 'Lab Number 5' in the film is an old map of the town of Bolton in England.
Even though they are much older now than when they first dubbed the original Full Metal Alchemist television series, Vic Mignogna (Edaward Elric) and Aaron Dismuke (Alfonse Elric) returned to dub for the English track.