Write What You Know: Dennis was inspired by and named after Hank Ketcham's son Dennis Ketcham, who was four years old when he conceived the strip. Henry and Alice Mitchell are also named after Hank Ketcham himself ("Hank" being a nickname for "Henry") and his first wife Alice, the real Dennis's mother.
The current version of the show, which debuted in 1992 replaces the original opening and ending sequences in all but one episode. Moreover, this carries over to the DVD releases.
When the series aired on Fox Family in the late 90s, the original opening was used, albeit shortened to allow more time for commercials. A commercial break was added in the middle of the second segment and the original bumpers were edited out along with compressed credits.
Rescued for the original 1986 series. Mill Creek Entertainment released it in its entirety in September 2016 after releasing the first season two years earlier. Up until that point, only a few individual segments were released on VHS and DVD.
Twelve episodes of the 1993 series were released in 2004 in Australia but they're now out of print.
Meaningful Release Date: In "Lean Green Jumping Machine", Dennis and his pals meet a man with a strong resemblance to Mark Twain and his works are featured prominently in the episode. Halley's Comet visited Earth in 1835 (the year Twain was born), 1910 (the year Twain died) and 1986 (the year this episode aired).
Recycled Script: The 1993 series episode, "Dennis the Genius" uses a similar premise to the The Simpsons episode, "Bart the Genius"; in both episodes, a troublemaking young boy (Dennis, Bart) cheats on their intelligence test by using the answers of their smarter friend (PeeBee, Martin) and get accepted into a school for gifted students, but soon find out that it's not as great as they wanted it to be. By the end of both episodes, they confess that they cheated on their tests to get sent back to their old schools.
Billing Displacement: Christopher Lloyd (as Switchblade Sam) is top-billed on the posters, followed by Joan Plowright (Martha Wilson), Lea Thompson (Alice Mitchell), Paul Winfield (the Chief of Police)... and then Mason Gamble andWalter Matthau, who only play, er, Dennis and Mr. Wilson.
Enforced Method Acting: Joan Plowright wasn't shown beforehand what Walter Matthau looked like after Mr. Wilson is covered in flour, so the first time she opened the door, she immediately burst out laughing, ruining the take.
Follow the Leader: This film was one of several movies about mischievous young boys made following the success of Home Alone. The late John Hughes wrote both films.
Real-Life Relative: Mason Gamble's actual sister Casey has a bit part as a neighborhood kid playing hide and seek.
Role Reprise: In the Japanese dub, Dennis is voiced by the late Takako Sasuga, who was the second voice actress who dubbed him in the dub of the 1959 TV series.
Billing Displacement: For the first three years, the credits featured Jay North by himself, and then one screen with three credits in the order of Herbert Anderson (Henry), Gloria Henry (Alice), and Joseph Kearns (Mr. Wilson). When Gale Gordon joined the cast, he became the second person to be credited, followed by Anderson and Henry.
Character Outlives Actor: George Wilson, following his portrayer Joseph Kearns' death in 1962, midway through the third season. Immediately after his death and a brief hiatus to mourn Kearns' passing, two scripts where Wilson was non-essential were hastily re-written, with substitute characters added and no mention of Mr. Wilson made. Later in the season, it was explained that George had business out east, and his brother, John (Gale Gordon) was brought in to "house sit". Early in the fourth season, the Wilsons (offscreen) moved to the East Coast, leaving John the new homeowner … and it was still presumed that George was alive when the series ended in 1963.
Creator Backlash: Jay North was put through the wringer on the show, never getting a moment's peace between the show itself, various crossover appearances in other sitcoms and even films, and commercials for their various sponsors, plus keeping up with school. Combined with the death of Joseph Kearns, the abuse he suffered from his aunt when he would "make mistakes", and his beginning to seriously age out of the role, he was tremendously relieved when it was cancelled.
Recycled Set: The set used for the Mitchell's house was originally made for the 1935 movie Party Wire, and was repurposed as the Stones' house on The Donna Reed Show before it was used on this show.
was planned, but never released.