Jane Kaczmarek, in real-life, has given birth by way of Caesarian section three times. When it came time to simulate giving birth without a C-section in the episode "Baby Part Two", Kaczmarek just imitated every other birth she had seen on television.
After the show ended, Bryan Cranston went on to be in the critically acclaimed series Breaking Bad (2008). On the last season DVD of Breaking Bad (2008), there is an alternate ending that involves Cranston, playing Hal from this show, waking up from a nightmare, which happened to be the events of Breaking Bad (2008).
Although the family's surname was revealed as Wilkerson in the pilot episode, it was decided afterwards that the family should not have a last name. A running joke on-set was that the family's last name was "Nolastname". This is officially confirmed in the final episode, "Graduation", when Francis drops his work pass, and his surname is briefly seen. Further confirmation can be seen when Malcolm is introduced to the stage for his speech. His last name is not heard, as the microphone screeches at the crucial moment, but you can read the announcer's lips clearly saying "Malcolm Nolastname".
The character of Francis would all but disappear from the show entirely starting with season six. For the final two seasons, Francis appeared in less than ten out of the forty-four aired episodes, despite the fact that Christopher Masterson remained in the opening credits. The character itself was changed significantly, going from the significant strides he had made to land a great job, and become a responsible young adult, to once more returning to delinquent, manipulative and two-timing behavior. Christopher Masterson during this time, took more of an interest in the production of the show, as he directed and wrote for much of seasons six and seven, rather than appearing as his character.
The hamster that Dewey (Erik Per Sullivan) releases in an earlier episode of the series can be seen in various episodes afterward, rolling past the screen (in its exercise ball) on the ground in the background.
When Francis was given a more diminished role in seasons six and seven, the show changed focus entirely. Rather than splitting episodes between a Malcolm story, with Francis side story, Hal and Lois instead became the primary focus of the show, with side-stories being reserved for Malcolm, Reese, and Dewey. Francis no longer appeared in his own stories, and instead became only an occasional recurring character.
In the opening credits, the boxer who inadvertently knocks out the referee is Pedro Cardenas, fighting Willie deWit. He accidentally KO'ed referee Bert Lowes during the 1982 North American Championships in Las Vegas.
In the episode where Hal and the boys go to the race track, they come home to discover that Lois had gone through all of their stuff, in that pile was a pack of Morley cigarettes, the same fake brand the Cigarette Smoking Man prefers to use on The X-Files (1993).
Scenes from One Million Years B.C. (1966) can be seen during the opening credits. In one of them, Raquel Welch is shown in the claws of a monster bird. The other scene shows the fight against a giant turtle.
Bryan Cranston did several of his own stunts. Besides the cartwheel and the headstand, Cranston did his own roller disco skating, spending all the free time he had in the week and a half he had to learn how to skate. After one of the show's writers asked jokingly whether Cranston would be willing to wear a suit of live bees, Cranston said he would, so they wrote a script around the idea (The Bots and the Bees). He ended up covered in ten thousand bees, and only got stung once.
Patrick Bristow first appears in the episode "Ida's Boyfriend" as Phillip, the head of the acting troupe hired to hold a Murder Mystery at the Grotto. Later, Patrick Bristow returns to the show as Lloyd, Chad's father in the episode "Chad Sleeps Over".
The part of Malcolm was originally written to be nine years old, so Frankie Muniz, being thirteen at the time, thought he was too old. He even gave his mother a thumbs down as soon as he came out of the audition room. The producers decided to make Malcolm around the age of twelve, and give Muniz the part. When the young actor found out he got it, he jumped on the hotel bed.
None of Malcolm's family have a last name. While in military school, Francis was referred to only as "Francis" and never by his last name. Reese joins the Army, and we learn the last name of his fake ID is "Jetson". There are no indications that the family has a last name, except in the pilot when Francis is talking on the phone to his family, you can see his name tag on his Marlin Academy uniform is "Wilkerson", but people often joked and called the family "Nolastname".
Many actors and actresses played double roles. For example, in season one, the episode "Therapy", Ms. Gilbert, the school therapist is also the administrator in the episode "Church" later on in the series, in season four.
Jason Alexander appeared on a season four episode about chess, as a man who claims to sell toner. He also appeared on Friends (1994). He is the man, to whom Phoebe tried to sell toner, only to find out he wants to commit suicide.
In season four, episode eighteen, "Reese's Party", while Hal and Lois are out of town, a meth lab is set up in the garage against the will of kids. Bryan Cranston goes on to become the meth kingpin in Breaking Bad (2008).
The opening sequence makes reference to eleven movies and television shows. In order, these are: 1) Three women fighting a giant turtle: One Million Years B.C. (1966). 2) Animé guy smiling in the rain: Shinri Shiogami from Nazca (1998). 3) Monster coming out of the ocean: The Kraken from Clash of the Titans (1981). 4) Woman being held above a nest of pterodactyl: another scene from One Million Years B.C. (1966). 5) Animé Guy Skateboarding: another scene from Nazca (1998). 6) Mud Monster grabbing a woman away from her boyfriend: Creature from the Haunted Sea (1961). 7) Skiing guy jumping off of a mountain in flames: Thrill Seekers (1999). 8) Wrestling Match: Bret Hart wrestling Chris Benoit during the WCW World Heavyweight Championship Match at WCW Mayhem PPV. 9) Robot head being put together: Out of the Unknown (1965). 10) Man Beating Brain Monster with Axe: The Brain from Planet Arous (1957). 11) Boxer knocking out referee: Pedro Cardenas fighting Willie DeWitt but accidentally KO'd referee Bert Lowes instead (1982 North American Championships in Las Vegas).