In preparation for his role, Daniel Day-Lewis lost thirty pounds and spent nights in the jail cell on the set as crew members threw water and verbal abuse at him.
In real life, Gerry Conlon and Giuseppe Conlon did not share a prison cell and were usually kept in separate prisons.
Daniel Day-Lewis kept his Northern Irish accent on and off the set for the entire shooting schedule.
Despite playing father and son, Pete Postlethwaite was only eleven years older than Daniel Day-Lewis.
Despite his executive producer credit, Gabriel Byrne distanced himself from the project, chiefly due to the enormous liberties taken with the details of the story by Jim Sheridan.