In the small town of Endora, Iowa, Gilbert Grape (Johnny Depp) is busy caring for Arnie (Leonardo DiCaprio), his mentally impaired younger brother who is turning 18, as they wait for the many tourists' trailers to pass through town during an annual Airstreamers' Club gathering at a nearby recreational area. His father had hanged himself seventeen years earlier,[3] and since then his mother, Bonnie (Darlene Cates), has spent most of her days on the couch watching television and eating. With Bonnie's morbid obesity leaving her unable to care for her children on her own, Gilbert has taken responsibility for repairing the old house and being protective of Arnie, who has a habit of climbing the town water tower as well as trees, while his sisters Amy (Laura Harrington) and Ellen (Mary Kate Schellhardt) do the other housework. A new FoodLand supermarket has opened, threatening the small Lamson's Grocery where Gilbert works. In addition, Gilbert is having an affair with a married woman, Betty Carver (Mary Steenburgen).
A young woman named Becky (Juliette Lewis) and her grandmother are stuck in town when the International Harvester Travelall pulling their trailer breaks down. Gilbert's unusual life circumstances threaten to get in the way of their budding romance. In order to spend time with Becky to watch the sunset, Gilbert leaves Arnie alone in the bath. He returns home late and finds that Arnie is still in the bath the following morning, shivering in the now cold water; his guilt is compounded by his family's anger and Arnie's subsequent aquaphobia. His affair with Betty ends when she leaves town in search of a new life following her husband's death; he drowned in the family's wading pool after having a heart attack. Becky becomes close to both Gilbert and Arnie. While they are distracted during one of their talks, Arnie returns to the water tower that he is always trying to climb. Arnie is arrested after being rescued from the top of the tower, causing his mother — who has not left the house in over seven years — to become the laughing stock of the town as she goes to the police station, forcing Arnie's release.
Soon after, Arnie ruins two expensive birthday cakes, tries to run away from his bath and in his frustration, Gilbert finally snaps, hitting Arnie several times. Guilty and appalled at himself, Gilbert flees and drives away in his truck. Arnie also runs out and goes to Becky, who takes care of him for the evening and helps him overcome his aquaphobia until he is picked up by his sisters. After some soul searching aided by Becky, Gilbert returns home during Arnie's 18th birthday party to make amends to his family for running out and receive Arnie's reluctant forgiveness. He also apologizes to his mother for his behavior and vows not to be ashamed of her or let her be hurt anymore. She acknowledges how much of a burden she has become to the family, and he forgives her. He introduces her to Becky — something he had been reluctant to do earlier.
Following the party, Bonnie climbs the stairs to her bedroom for the first time since her husband's suicide. Arnie later tries to wake her but discovers that she has died. With no way to remove her body from the second floor that evening, the police make plans to return with a crane the next day. To protect Bonnie's dignity, the family empty the home of possessions and set fire to it, burning it to ashes with their mother's body inside.
A year later, Amy gets a job managing a bakery in the Des Moines area while Ellen looks forward to switching schools and living in a bigger city. Gilbert waits by the side of the road with Arnie, now turning 19, waiting for the tourist trailers to come around again. As part of the convoy, Becky arrives with her grandmother and picks them both up.
Johnny Depp as Gilbert Grape
Leonardo DiCaprio as Arnold "Arnie" Grape
Juliette Lewis as Rebecca "Becky"
Mary Steenburgen as Elizabeth "Betty" Carver
Darlene Cates as Bonnie Grape
Laura Harrington as Amy Grape
Mary Kate Schellhardt as Ellen Grape
Kevin Tighe as Kenneth "Ken" Carver
John C. Reilly as Tucker Van Dyke
Crispin Glover as Robert "Bobby" McBurney
Penelope Branning as Becky's Grandma
Libby Villari as the Waitress