To live the role, Viggo Mortensen would sleep in his clothes and deliberately starve himself. At one point, he was thrown out of a shop in Pittsburgh, because they thought he was a homeless man.
Viggo Mortensen nearly turned down the role of Man, because he had planned a break from film work. After completing his work as Man, Mortensen took roughly two years off from acting.
Director John Hillcoat filmed the soft drink vending machine scene with Man and Boy several times, each with a different brand beverage, out of concern that Coca-Cola executives would not want their product to appear in this movie. A telephone call, from Viggo Mortensen to the President of Coca-Cola, secured permission for a can of Coca-Cola to appear, consistent with the source novel.
The ocean scene was Lake Erie.
During a preview Q&A screening in London, John Hillcoat revealed that Kodi Smit-McPhee won the role of "The Boy", partly due to an audition tape sent in by Kodi's father that showed them re-enacting the scene where the father shows the boy how to kill himself, by placing a pistol in his mouth.