During the filming of a strip sequence, Gerard Butler's suspenders hit Hilary Swank on the forehead. She received a cut and had to be taken to a hospital, where she received several stitches.
According to the Christmas 2006 issue of People magazine, Jeffrey Dean Morgan had to learn to play the guitar for his part in this film in a very short time. His guitar instructor was Nancy Wilson of the band Heart. Morgan was thrilled to take lessons from her, because, in his own words, "I had such a crush on her as a kid."
Gerard Butler later had to apologize to Irish fans in particular for his poor attempt at an Irish accent.
The whole letter Gerry sent to his mom and dad in Ireland says: "Dear Mum & Dad. Well, Doc says there's not much time, so I thought I'd write to you, seeing how bad we Kennedy's are with modern day contraptions like telephones. Tell Dad to not lay about, and to take care of his legs-keep them walking. I always think of Dad walking across the farm yelling after the hands too lazy to keep the chickens fed. And you Mum, yelling at Dad to treat the boys with a Father's hand, not a father's belt. I remember everything Mum. And I thank you for giving me a mother's breath of life and love. No son ever loved a mother more, I can tell you that. Never could say it to your face. Nor to Dad. But I love you."
Even though the plot of the film is quite different from the novel, all the letters are identical.