Miss Jolie, who is the estranged daughter of actor Jon Voight, has said she did not see the point of giving birth herself when there were so many unwanted children in the world.
'I like to think that with every adoption I save another child from the orphanage,' she said.
The adoption of Maddox was not without difficulties.
While she and Thornton were awaiting immigration approval, the U.S. halted adoptions from Cambodia following allegations of baby selling involving Westerners.
Only when the ban was lifted were the couple able to take custody of Maddox.