Steven Spielberg was the film's executive producer and the screenplay was written by Chris Columbus. The film stars Zach Galligan and Phoebe Cates, with Howie Mandel providing the voice of Gizmo, the main mogwai character. Gremlins was a commercial success and received positive reviews from critics. However, the film was also heavily criticized for some of its more violent sequences. In response to this and to similar complaints about Indiana Jones and the Temple of Doom, Spielberg suggested that the Motion Picture Association of America (MPAA) alter its rating system, which it did within two months of the film's release.
While searching for a Christmas present for his teenage son, Randall Peltzer (Axton) discovers a small, furry creature called a Mogwai in an antique store in Chinatown. The owner of the store refuses to sell the Mogwai on the grounds that owning one is too great a responsibility. However, as Randall is leaving the store, the owner's grandson (Louie) sells Randall the creature, stating that the family needs the money. The boy gives Randall three specific instructions in caring for the Mogwai: never expose it to bright light (especially sunlight, which will kill it); never get it wet (which will make it multiply); and, most importantly: never, ever feed it after midnight. Randall takes the Mogwai to his family in the town of Kingston Falls; being an inventor, he names the creature "Gizmo".
The following evening, Randall gives Gizmo to his son Billy (Galligan) and tells him the three rules he must obey. A glass of water is accidentally spilled on Gizmo, causing him to convulse and produce five new creatures from his own body. One of the creatures, dubbed Stripe for his white quiff of hair, acts as their leader, but is very hostile to Gizmo. Curious to learn more about the creatures, Billy takes Gizmo to his science teacher, Mr. Hanson (Turman), and produces a sixth new creature. Leaving the new creature with Mr. Hanson, on which he will conduct tests, Billy returns home, and the other five creatures trick him into feeding them after midnight by biting the cord of his alarm clock. In the morning, Billy discovers the creatures have turned into cocoons. Gizmo, having virtuously refused the food earlier, remains unchanged.
In the meantime, the sixth creature steals Hanson's sandwich and cocoons itself. Later, it hatches and breaks out of its cage, hiding in the dark corners of the room. Hanson tries to reason with it and bribe it with a candy bar, but the creature eats it and attacks Hanson. Billy arrives and finds the creature has turned into a reptilian monster. Elsewhere, the other Mogwai have hatched into "gremlins", mischievous reptilian monsters with sharp teeth and claws. They attack Billy's mother (McCain), who is able to escape with Billy's help, and the gremlins are killed. Stripe escapes and leaps into a swimming pool, creating hundreds of new gremlins who go on a rampage throughout town. Billy and Gizmo rescue Billy's girlfriend Kate Beringer (Cates) when the gremlins overrun the tavern where she works. Billy, Kate, and Gizmo discover that the gremlins have temporarily stopped their rampage and have assembled in the local movie theater to watch Snow White and the Seven Dwarfs. The three set off an explosion that kills the gremlins and destroys the theater, but their celebrations are cut short when Kate spots Stripe in the window of a nearby Montgomery Ward store.
Billy follows and battles Stripe, who leaps into a water fountain intending to multiply again. Before he can multiply, Gizmo opens a set of window blinds, causing sunlight to pour into the store, killing Stripe. As the Peltzers recover from the rampage, the antique store owner arrives to claim Gizmo, claiming that the Western world is not yet ready for the responsibilities that come with caring for a Mogwai, but that Billy may someday be ready to properly care for Gizmo.
- Zach Galligan as William "Billy" Peltzer
- Phoebe Cates as Kate Beringer
- Hoyt Axton as Randall "Rand" Peltzer
- Frances Lee McCain as Lynn Peltzer
- Corey Feldman as Pete Fountaine
- Keye Luke as Mr. Wing (credited as "Grandfather", Mr. Wing's name is revealed in the 2nd film)
- John Louie as Mr. Wing's grandson
- Dick Miller as Murray Futterman
- Jackie Joseph as Sheila Futterman
- Polly Holliday as Mrs. Ruby Deagle
- Judge Reinhold as Gerald Hopkins
- Edward Andrews as Mr. Roland Corben
- Glynn Turman as Mr. Roy Hanson
- Belinda Balaski as Mrs. Joe Harris
- Scott Brady as Sheriff Frank
- Jonathan Banks as Deputy Brent
- Harry Carey, Jr. as Mr. Anderson
- Chuck Jones as Mr. Jones, Billy's drawing mentor
- Kenny Davis as Dorry
- Nicky Katt and Tracy Wells as Schoolchildren
- Mushroom as Barney
- Frank Welker as Stripe
- Howie Mandel as Gizmo
- Don Steele as Rockin' Ricky Rialto
- Marvin Miller as Robby the Robot (uncredited)
- Jim McKrell as Lew Landers, TV News Reporter
- Steven Spielberg as Man riding Recumbent bicycle (uncredited)
- Jerry Goldsmith as Man in Phone Booth Looking at Camera (uncredited)
- William Schallert as Father Bartlett (uncredited)
- Tom Bergeron as TV News Reporter (uncredited)
- Kenneth Tobey as Mobile Gas Station Attendant (uncredited)