Shared with you
After Swigert admits having forgotten to file his tax return, Clint Howard, who has had tax problems in real life, improvised the line where he says "That's no joke! They'll jump on him!"
In a commentary track, Marilyn Lovell comments that Tom Hanks exactly portrays Jim Lovell's mannerisms and style of movement.
In some scenes where the Earth can be seen from the windows of Apollo 13, it is one of the photos taken by Jim Lovell and Bill Anders on the Apollo 8 mission.
Bill Paxton, Tom Hanks and Kevin Bacon were all very proud of the fact that they weren't sick on the so-called Vomit Comet - the plane used to simulate zero gravity. The cameramen weren't so lucky.
Jim Lovell wore his old Navy Captain's uniform in the scene where he greets the astronauts aboard the U.S.S. Iwo Jima. When Ron Howard asked Lovell if he'd like to be in the film as the ship's Admiral, Lovell agreed, but pointed out, "I retired as a Captain; a Captain I will be."