The film follows the fictional family, the Stupids, with a last name synonymous with their behavior. The story begins with patriarch Stanley Stupid believing "sender" from letters marked "return to sender" is a wicked man planning a conspiracy. Adding several misunderstandings, the family unwittingly saves the world from military chaos, while believing a fake story about a fictional man named Sender and his plot to confiscate everyone's mail and trash.
Joan and Stanley Stupid are convinced they are victims of a conspiracy that steals their garbage every week and in an attempt to uncover this, Stanley follows the garbage truck to the city dump where he stumbles across Lieutenant Neidermeyer who is selling contraband weaponry to a group of terrorists. Neidermeyer believes Stanley to be a secret agent who has uncovered their operation and orders him assassinated, and after several attempts on his life result in him unintentionally killing his would be assassins, Stanley narrowly escapes a carbomb and is presumed dead by Neidermeyer.
Meanwhile, the children, Buster and Petunia Stupid, believe their parents have been kidnapped by a Chinese restaurant and go in search of them. They reunite with their mother Joan, who explains her theory that the police have turned against them and are responsible for their missing father.
Once all the family are reunited back home, Joan tells the children about their father's last job for the postal service where he discovered all the letters being marked "return to sender", but was fired before he could find out who "Mr. Sender" was. Stanley tells the family about the conspiracy theory he has invented that combines all the ideas the family's overactive imaginations have created, including the "Evil Mr. Sender" plotting to steal all the mail and garbage from America and employing the police to kidnap anybody who discovers his scheme. When they find local museum curator Charles Sender in the phone book they set off in pursuit, ultimately tracking him to a television studio where Stanley appears on a talk-show and is spotted by Niedermeyer who has him kidnapped and brought to his army base.
While being held hostage at the army base Stanley overhears the address of the warehouse being used for the illegal arms deals. Following a fluke escape the entire Stupid family head to the warehouse where they expect to find Sender and the stolen mail. The family confront Neidermeyer and his terrorist associates in a slapstick battle, resulting in some large explosions that cause the police to investigate the warehouse. Stanley offers what he perceives to be heroic advice about how Sender can repent his evil ways but Sender takes them as road directions and both men are pleased with the outcome of the conversation.
The family arrives home and resolving some subplots including a delivery driver finally getting the order Joan placed to them and saving them from Neidermeyer one last time in the process, as well as some extraterrestrial pilots attempting to kill Stanley who, in his usual manner, unwittingly dispatches them.Tom Arnold as Stanley Stupid
Jessica Lundy as Joan Stupid
Bug Hall as Buster Stupid
Alex McKenna as Petunia Stupid
Mark Metcalf as Colonel Neidermeyer
Bob Keeshan as Charles Sender
Christopher Lee as Evil Sender
Matt Keeslar as Lieutenant Neal
Frankie Faison as Lloyd
David Ferry as Late-night show host
Rolonda Watts as Talk show hostess
Max Landis as Graffiti artist
George Chiang as Chinese Waiter #1
Jenny McCarthy as Glamorous actress
Atom Egoyan as TV studio guard
Norman Jewison as TV director
Robert Wise as Stanley's neighbor
David Cronenberg as Postal supervisor
Gillo Pontecorvo as Talk show guest
Costa-Gavras as Gas station attendant
Gurinder Chadha as Reporter #1
Mick Garris as Reporter #2
Harvey Atkin as Deli Guy
Stanley Stupid and his daughter enter a planetarium and believe they are dead. The janitor talks to them and they believe he is God. They call him Lord, and he corrects them saying his name is Lloyd, and they refer to God as "Lloyd" from then on. The gag is further extended when they are "rescued" by a takeout-delivery man who works for Floyd's Restaurant. They believe he is a guardian angel and assure him that he works for Lloyd, not Floyd. The gag appears in the closing credits, when a final title says "Trust In The Lloyd".
The Stupids' dog, Kitty, and cat, Xylophone, are anthropomorphized- claymation characters that act much more intelligently than their owners. For instance, they solved the "mystery" of why the car wouldn't start. Far from needing the mouth to mouth resuscitation Stanley provided, the problem was that the car keys weren't in the ignition.
Another gag is the name of the film's main antagonist, Colonel Neidermeyer, played by Mark Metcalf, who had previously played Doug Neidermeyer in Animal House.
Many smaller roles and bit parts are filled by acclaimed film directors, including Atom Egoyan, Norman Jewison, Robert Wise, David Cronenberg, Gillo Pontecorvo, Costa-Gavras, and Gurinder Chadha.
The film was shot in Toronto, Ontario (Downtown shots) and Uxbridge, Ontario (Home located at 55 Quaker Village Drive, Uxbridge, Ontario).
This was the last film produced by Savoy Pictures.
The Stupids grossed $2,491,989 in North America from an estimated $25 million budget.
Review aggregation website Rotten Tomatoes gave the film a score of 21% based on 14 reviews.
Arnold won at the 1996 Golden Raspberry Awards - Worst Actor for his performances in Big Bully, Carpool, and The Stupids. The Stupids was also nominated for the award for Worst Picture, Worst Director (John Landis), and Worst Screenplay (Brent Forrester).