- Accidentally Correct Writing: Despite coasting along on Rule of Cool, the show sometimes got something right even when the writers obviously weren't even aiming for accuracy. One such highlight occured in Sorry, Wrong Era when Jimmy shattered the big diamond in an attempt to break off a chunk small enough for his jury-rigged Bamboo Technology time-warping device. Diamond, while certainly the hardest natural substance on earth, is also brittle enough to shatter using little more than a hammer, chisel, and a little bit of precision.
- Banned in China: The Arabic version of the show removes pretty much anything that hints at there being anything more than just plain friendship between child characters. It's done in such a crude manner that entire scenes are reduced to just a few lines of dialogues with an awkward transition to the next and some of the more Ship Tease prone episodes end up downright incomprehensible.
- Cross-Dressing Voices:
- Debbie Derryberry as Jimmy.
- Also, Candi Milo as resident bad boy Nick.
- Early Draft Tie-In: The game for Attack Of The Twonkies uses Cindy's design from the movie instead of her older looking, pigtail-less design from the actual series.
- He Also Did: Mark DeCarlo, voice of Hugh Neutron, was a lot winner on the 1980s NBC run of Sale of the Century, hosted the relationship game show Studs in the early 90s, and currently appears on ABC's The Chew.
- Keep Circulating the Tapes: Surprisingly enough, given the show's popularity. To date, there have been no complete series releases of this show on DVD, and not every episode has been released on home media - the DVD releases it did get are compilations of episodes. Thankfully, it airs in reruns on the Nicktoons channel every once in a while, and all of the episodes can be found online on places such as Hulu and Amazon Instant Video as well.
- Life Imitates Art: "Retroville 9", aired 2003, shows Jimmy & Co. going to Nagoia, Japan to participate in the "Junior Baseball World Championships". No such tournament existed back then but a 12U Baseball World Cup was founded in 2011, with a 15U equivalent coming up the following year. Seeing as that was a Season 2 episode, Jimmy and others would have qualified for the former. Japan being the tournament's host also makes sense as baseball is a very popular sport there.
- Non-Singing Voice: Meldar from "Win, Lose, and Kaboom" had his speaking voice done by Tim Allen, but his singing voice was provided by Jess Harnell.
- The Other Darrin:
- King Goobot and Ooblar were voiced by S. Scott Bullock and Paul Greenberg in the original pilot. Patrick Stewart and Martin Short replaced them for the movie, but Bullock and Greenberg reprised their roles for the series. In the 2002 video game, they were voiced by Joe Whyte and Mark DeCarlo respectively.
- Ultra-Lord was voiced by Jim Cummings in the film and series but was voiced by Rob Paulsen in the 2001 PC video game.
- The mayor of Retroville was voiced by Mark DeCarlo in the episode "Normal Boy" and by Jim Cummings in all subsequent appearances.
- Tee of the alien bandit trio was originally voiced by Maurice LaMarche, who also voiced Zix, but Kevin Michael Richardson started voicing the character in "The Incredible Shrinking Town" and onward.
- Sheen's dad went from being voiced by Carlos Alazraqui in the movie to being voiced by Joe Lala in the series.
- Recursive Adaptation: Attack of the Twonkies- originally a spinoff game- got its own special that majorly diluted the game's plot. The twonkies became a Canon Immigrant after this, appearing every now and then as an Easter Egg.
- Saved from Development Hell: The original storyboard was created in the 1980s. It was later revived as a 40-second test animation called The Adventures of Johnny Quasar in 1995, and later again as a short called Runaway Rocketboy in 1998. The 1998 incarnation was picked up by Nick a few years later and thus the film was made.
- Troubled Production: According to one of the people who worked on the show, the show had INSANE deadlines (they only had three weeks to slam together each episode!)
- What Could Have Been:
- The earliest pilot animation was going to be called The Adventures of Johnny Quasar. A test animation was created, but not much else came from it. Early designs were very different from the final such as Jimmy's parents◊ and friends◊, (with an unknown character holding a basketball) but not Goddard, much◊. In the short, the neutron logo was a "Q" design instead of an atom design.
- Libby was a last minute inclusion but she looked very different at one point.
- The main theme was slightly longer with a couple more lyrics.
- There was going to be an Ultra Lord spinoff, but it never came to be◊,but the idea for a spin-off became Planet Sheen.
- According to the show's page on The Other Wiki, there was going to be a fourth season, which would've been Darker and Edgier. First, the season premiere episode "Deep Impacts" would've shown Jimmy's Final Battle with Evil Jimmy. Another episode would feature Cindy and Betty interacting with each other, Cindy and Jimmy would've finally become a couple, and Nick, who was basically Demoted to Extra in the show, would've gotten a larger role. Finally, there were going to be more appearances from the League Of Villains.
- Writing by the Seat of Your Pants: DNA Productions had a mere three weeks to slam together each half-hour episode.
Trivia / The Adventures of Jimmy Neutron: Boy Genius