The film was directed by Nick Castle, written and produced by John Hughes, and distributed by Warner Bros., which released the film under its Family Entertainment banner. It concerns the misadventures of a mischievous child (Mason Gamble) with a cowlick and a grin who wreaks havoc on his next door neighbor, Mr. Wilson (Walter Matthau), usually hangs out with his friends, Joey (Kellen Hathaway) and Margaret (Amy Sakasitz), and is followed everywhere by his dog, Ruff.
A direct-to-video sequel called Dennis the Menace Strikes Again was later released in 1998 without the cast members from this film. The film was also followed by a Saturday morning cartoon series called All-New Dennis the Menace.
Plot: Dennis Mitchell is a five-year-old boy who lives with his parents Henry and Alice, and is the bane of next door neighbor George Wilson's existence. The movie opens with George getting the newspaper, but flees inside at the sound of Dennis on his bicycle. He gets into bed and pretends to sleep. Dennis enters, concludes George is sick from the prescription bottles on his nightstand, and tries to feed him an aspirin by shooting it down his throat with a slingshot. George, choking, spits out the aspirin as Dennis returns home. With his parents both busy, Dennis is forced by his mother into joining his friend, Joey, at Margaret's house, whose mother volunteered to watch them for the day. Dennis begs not to, as Margaret is mean to him. When they arrive, Dennis, Joey, and Margaret venture into the woods to an abandoned tree house and intend to fix it up. Later, while getting paint from a high shelf in the garage, Dennis tries to grab his slingshot, which was taken away from him, accidentally spilling the paint on the ground. While using a vacuum to clean it up, he also sucks in a few twigs when he goes outside, causing a blockage, switching the suction from 'in' to 'out'. A blob of paint and twigs flies into George's grill, which he is using to barbecue lunch.
Dennis's parents arrange for a babysitter named Polly and her boyfriend Mickey to watch him for the night, but repeated doorbell ditches from him push the two too far (not knowing he is behind them), and they end up pulling a prank on George when he rings the doorbell to scold Dennis after finding paint and wood in his food from the earlier incident. Meanwhile, a burglar named Switchblade Sam (never named in the film, only in the end credits) arrives in town and begins robbing houses, as well as striking fear into the children that he meets.
Dennis' parents are both called away on business trips, and when everyone they know refuses to look after him (due to their experience with the boy's unintentionally trouble-making behavior), they turn to George and his wife Martha. Martha loves Dennis and sees him as a surrogate grandson, as they never had children. George is further irritated by him spilling bath water on the bathroom floor, replacing George's nasal spray with mouthwash, and his mouthwash with toilet cleanser, and bringing his pet dog, Ruff, into the house for a while. Dennis also sees George's collection of gold coins, in a bookshelf safe, and deduces that it uses the house's address as a combination lock. As a longtime member of the local garden club, George is chosen to host the Summer Floraganza. He is excited to have this honor, as he has been growing and nurturing a rare night-blooming mock orchid for forty years. George notes that after growing for the said length of time, the plant's flower will finally bloom, only to die several seconds later.
Alice gets stuck at the airport due to a storm, thus forcing Dennis to stay with the Wilsons for an extra night, which coincides with the unveiling of the plant and its one-time blooming. While the Floraganza begins, a bored Dennis pushes a black button, which turns out to be the garage door opener, causing the dessert table in front of the garage door to be overturned. Irate, George sends Dennis inside. When Dennis hears Switchblade Sam robbing the house, he goes downstairs and finds George's gold coins missing. He runs outside to tell him just as the flower is beginning to bloom, which causes George and all the guests to miss its entire lifespan. George severely scolds Dennis, tells him that he doesn't want to see or know him anymore, and to get out of his way. Shortly thereafter, a tearful Dennis gets on his bicycle (with a wagon attached) and rides off into the night, eventually bumping into Switchblade Sam in the woods. Sam abducts him, intending to use the child as a hostage.
Dennis' parents return home and learn of his departure, and they, the authorities, and his friends (Joey, Margaret, Gunther and all the neighborhood kids) start an intense search. George joins them, as he now feels intense guilt and remorse over the harsh things he said to Dennis. However, Dennis unintentionally but effectively defeats Switchblade Sam by tying him up and handcuffing him (trying to show Sam good knot tying), losing the key (by force feeding it to Sam from a kettle of baked beans), and repeatedly setting him on fire, amongst other things. He returns to George's house the next morning with Switchblade Sam in his wagon, having also recovered George's gold coins, and Sam is taken into police custody. Dennis and George make up, and the Mitchells and Wilsons become friends on better terms. That night, George explains that he's learned some things about children: "Kids are kids, you have to play by their rules, if you can't do that, you're headed for trouble. You have to roll with the punches. You have to expect the unexpected." While Dennis is toasting marshmallows, one catches fire. He tries to douse it by whipping the marshmallow stick about, but the marshmallow flies off, still burning, and lands on Mr. Wilson's forehead.
The end credits are accompanied with Dennis sitting by a photocopier, having been kicked out of daycare at his mother's workplace. He asks to help an employee, Andrea, who comes to use the photocopier, but she says Dennis doesn't know which button to press. To show Andrea that he does know, Dennis whacks the "PRINT" button. Andrea's tie is sucked into the scanner and she is pinned face-down onto it. Dennis runs away screaming as the machine repeatedly scans Andrea and spews out photocopies showing her agonized facial expressions.