Cast the Runner-Up: Chuck Zito (Pancamo) first auditioned as a Biker, having being a veteran member of the Hell's Angels Biker Club. However because of his complexion and heavy New York accent, Tom Fontana thought he'd fit in better with the Italians on the series.
Jefferson Keane is executed halfway through the first season because the actor portraying him, Leon, refused to commit to a series. When Leon asked Tom Fontana why he was being killed off, Fontana told him it was because he said he wouldn't commit to more than four episodes. Leon replied that he thought he'd been talked out of that and actually wanted to stay.
Production Posse: A very large number of the actors also played main, recurring, or guest characters in the Law & Order franchise. This is likely because both series were filmed in New York rather than California, so it pulled from the same pool of actors.
Resident Manipulative Bastard Ryan O'Reily (played by Dean Winters) and his mentally retarded older brother Cyril O'Reily (Scott William Winters) are brothers in real life. Their eldest brother, Bradford Winters, was series creator/head writer Tom Fontana's main collaborator for most of the series' run, as well.
Terry Kinney (McManus) and Kathryn Erbe (Shirley Bellinger) were married for 13 years and have two children together.
Ernie Hudson's son Ernie Hudson Jr. made recurring appearances as inmate Hamid Khan.
J. K. Simmons' spouse Michelle Schumacher made guest appearances as Norma Clark. Their characters don't interact in any way, but Vern notes that Norma's letter is "stinking with cheap perfume" during a mail delivery scene.
Reality Subtext: Chuck Zito (Pancamo) and Craig muMs Grant (Poet) were the only cast members who had actually done time in prison.
Role-Ending Misdemeanor: Some cast members that played prisoners have noted that, throughout the series, if you showed up late to the set, your punishment would be that your character would either die or be raped the next week.
Romance on the Set: Terry Kinney and Kathryn Erbe were married in real life during the show. They divorced in 2006.
Technology Marches On: In season 3, one of the inmates writes his memoirs. He saves it on a disk, which is then intercepted. Today, the file would be sent via email or online submission form, and stored elsewhere.
Early in Season 5, Beecher's computer gets upgraded...to 128MB of RAM (which was slow even in 2002).
Wag the Director: According to Tom Fontana, Dean Winters had a crush on Luna Lauren Velez and requested a sex scene to be filmed with their characters. A scene in which O'Reily fantasizes about having sex with Nathan was filmed much to Winters' delight.
What Could Have Been: Tom Fontana said that Rick Fox would have been in more episodes if he'd played for New York Knicks instead of the Los Angeles Lakers.