A Boy and His Sister: A Dexter's Laboratory Movie

A Boy and His Sister (marketed as A Boy and His Sister: A Dexter's Laboratory Movie) is a 2026 American computer-animated adventure comedy film directed by Genndy Tartakovsky (creator of the original series) and written by series writers Paul Rudish, Amy Keating Rogers, Michael Ryan, and Walt Dohrn. Candi Milo, Kat Cressida, Eddie Deezen, Jeff Bennett and Kath Soucie reprise their roles from the series; accompanied by Mckenna Grace, Peter Capaldi, Charlize Theron, and Jim Parsons. This is the first computer-animated feature film from Cartoon Network Studios, with co-production by Warner Animation Group.

A Boy and His Sister had its premiere in Hollywood on March 25, 2026, and was released theatrically in the United States for the series' 30th anniversary on April 10, by Warner Bros. Pictures. It grossed $150.2 million on a $75 million budget. The film was met with positive reviews, with critics praising the voice cast, humor, and heart, while the choice of computer-animation was mixed.

Plot
Dexter, having graduated from Huber Elementary and moving to Huber University, is about to receive a Nobel prize for his invention that ends world hunger; an invention he had been working on in secrecy due to his childish older sister, Dee Dee, who had ruined several of his inventions from the start. Dee Dee, eavesdropping on Dexter's pursuits, was heartbroken but determined to sabotage his dreams. As the night of the ceremony had begun, Dee Dee had stopped the machine by spitting a wad a gum she was chewing during Mandark's showcase of his visual Mind-Screen invention. After Dexter's world hunger machine had made a good first impression, the machine spits out various amounts of food at the audience. Dexter fortunately stops the machine in time, but discovers the wad of gum in the gears which costs him the Nobel prize. In retaliation and realization that Dee Dee was responsible, Dexter blames her and starts a food fights with her.

After the ceremony, Dexter was disappointed and upset about his dream being crushed until he gets a call from the committee that one of their security cameras caught footage of Dee Dee spitting her gum into the gears as everyone was oblivious; exposing Dee Dee for sabotaging his machine and reinstating the Nobel prize to him. As Dee Dee was exposed, she ends up grounded for it. Dexter later enters her bedroom to take pity on her, whereas Dee Dee angrily explains that she hates the idea of him going to college and never got the childhood with him; Dexter apologizes for it, but he cannot pass up his second opportunity to start anew as a college student. The next day, the family visits Huber University, and Dexter is amazed by its facilities and classes to his liking. After the tour, he meets the Dean's daughter Marie and bonds with her over her interests in technology and video game developing, with his parents proud that he expands his social life.

Meanwhile, Mandark, walking the streets of Genius Grove, plans on going with his plan of annihilating Dexter; his former substitute teacher Professor Ian Adams helps him in his pursuit due to his hatred of Dexter as well. With Dee Dee, she and her parents are called to the elementary school and given word that Dee Dee is failing her classes and will be held back a grade if this continues, leaving her in utter dismay; suggesting she be tutored to help her get back on track, Dexter was chosen as an easy choice. During her tutoring, Dexter had thought about Dee Dee's words last night and decides to make it up to her by spending time and playing with her before his move to college next week. As the week was over, Dee Dee thanks him for bonding with her, with Dexter showing satisfaction from it.

As the family drives to the university, a laser, which was shot by Mandark and Adams in their mech, had almost hit them. Noticing Mandark in, Dexter addresses the mech his parents and they try to allude it through the city. Before they could go any farther, Adams shoots another laser which slices the family car in half, stopping them in their tracks. As Mandark was about to shoot Dexter, Dee Dee tosses throwable debris at the mech to distract them long enough for Dexter to escape and for their parents to go to the police. Irritated, Adams prepares to dispose of Dee Dee, but Mandark intervenes out of affections towards her, which has Adams eject him from the mech for his weakness and eliminate Dexter himself, then take over the city due to the ridicule from his peers. Before he goes to hunt down Dexter, he decides to kick Mandark away, which ends up with Dee Dee ending up kicked after she shoves Mandark out of the way. Mandark saves an injured Dee Dee and helps her save Dexter, as well as reluctantly promising her to stop his rivalry with him in return.

Dexter runs to the university and takes refuse with the students and employees who have heard about the mech on the news. Mandark and Dee Dee enter Dexter's lab to retrieve some of his equipment to rescue him, as well as using the Robo-Dexo 2000 for transport and safety. Adams finds Dexter at the university from the help of a newspaper headline of the latter's pursuits; Dee Dee arrives at the last minute and faces off with Adams while Mandark retrieves Dexter and sabotages Adams' mech by setting off the self-destruct feature he had installed. As Dexter was about to take over, Dee Dee ejects him out as she wants him safe and to make up for her actions. Mandark hides under Adams' mech and sets off the self-destruct feature via voice activation, with Dee Dee tossing the mech into the sky before it would explode. Dexter forgives Dee Dee for her recklessness and thanks her for rescuing him, along with choosing not to go to the university for the sake of spending the rest of his childhood with her, much to her delight. As the police arrive after their parents were told to contact, Adams had survived the explosion and plummets on one of the police car roofs before being arrested.

As time goes on, Dexter had begun a respecting bond Dee Dee after forgiving each other; expanded his social life from befriending Marie and forging a friendship with Mandark after the latter had ended their rivalry; and returned to Huber Elementary, working as a substitute teacher. Dee Dee had also begun a relationship with Mandark.

In a post-credits scene, Dee Dee enters Dexter's lab to call him for dinner. While searching for him, she finds and presses a button. As Dexter was exiting the bathroom, she finds Dee Dee covered in ashes telling him how she realizes how he felt when she destroyed his inventions, thus receiving a taste of her own medicine.

Voice cast
Gary Anthony Williams, Jim Cummings, Fred Tatasciore, and April Winchell provide additional voices.
 * Kat Cressida as Dee Dee, Dexter's oblivious but well-meaning sister.
 * Candi Milo as:
 * Dexter, Dee Dee's intellectual younger brother.
 * Grandpa O'Reily, Dexter and Dee Dee's grandfather and father to their mother.
 * Eddie Deezen as Mandark Astronomonov, Dexter's arch-rival with an infatuation towards DeeDee.
 * Jeff Bennett as:
 * Dexter and Dee Dee's father
 * "Windbear" Astronomonov, Mandark's father.
 * Kath Soucie as:
 * Dexter and Dee Dee's mother
 * Dexter's computer
 * Mee Mee, one of Dee Dee's friends.
 * "Oceanbird" Astronomonov, Mandark's mother.
 * Dextamina, Dexter and Dee Dee's great aunt.
 * Peter Capaldi as Professor Ian Adams, a former substitute teacher in Dexter's class who was ridiculed by the scientific community for his bogus findings. His name is a play on the word "ion atoms."
 * Jim Parsons as Dean Julius Dean, the dean of Huber University.
 * Mckenna Grace as Marie Dean, Jullius' video game-obsessed daughter who develops a quick bond with Dexter on electronics.
 * Charlize Theron as Denise Dean, Jullius' wife and Marie's mother.
 * Dan Aykroyd as Gary Zeh, the host of the Nobel Prize award ceremony.
 * Kimberly Brooks as Lee Lee, one of Dee Dee's friends.
 * Tom Kenny as Douglas E. Mordecai III, Dexter's closest friend.
 * Frank Welker as Phillips Luzinsky, a teacher of Huber Elementary.
 * John DiMaggio as:
 * Fergle O'Reily, Dexter and Dee Dee's uncle and brother to their mother. He was previously voiced by Mark Hamill in the series.
 * A head policeman who arrests Adams.
 * Christopher Walken as Granddad, Dexter's and Dee Dee's other grandfather who is the father of their father.

Development
The idea of feature film was pitched by Xavier Shaquille (creator of Knight School and co-director of The CN Movie) that had a story focused on Dee Dee being insecure about Dexter leaving for college and had wished for a childhood with him. He had wanted Genndy Tartakovsky on-board with the project as director and had chosen an array of old writers from the series to write the film, with Tartakovsky writing alongside them to bring the characters back to their early characterizations from the first two seasons.

The original cast members from the series reprise their roles for the film, while chosen cast members for the film's new characters consist of Mckenna Grace, Peter Capaldi, Charlize Theron, Jim Parsons, Dan Aykroyd and Mel Brooks.

Animation
Shaquille had chosen to have a Dexter's Laboratory feature film in computer-animation. He had chosen Sony Pictures Imageworks due to how the studio had animated Tartakovsky's Hotel Transylvania film series and believed they could recapture the animation from the series.

Music
Hans Zimmer and Steve Mazzaro were chosen after Shaquille had adored how they had captured the musical style to Nickelodeon's SpongeBob SquarePants in Nickelodeon Movies' The SpongeBob Movie: Sponge on the Run, another computer-animated film based on a popular animated series. Steve Rucker and Thomas Chase served as the music supervisors. The score was released via WaterTower Music on April 7, 2026.

The film also uses licensed music, notably Dean Martin's "That's Amore"; Phil Collins' "Sussudio"; by J Balvin and Willy William's "Mi Gente"; Pitbull's "Fireball"; and Sheryl Crow's "Grow Up". "Secrets" by will.i.am and "Sibling Rivalries" by De La Soul, which are songs from the compilation album Dexter's Laboratory: The Hip-Hop Experiment, are also used during the credits.

Theatrical
In commemoration to the series' 30th anniversary, the film released on April 10, 2026. The film had been marketed by various theaters to promote its policies during December 2025.

Home media
A Boy and His Sister was released on digital on June 16, 2026, then on Blu-ray and DVD on July 14. Its special features consist of a 10-minute behind-the-scenes featurette, character animation tests, an animation progression, a San Diego Comic-Con panel with Dexter and Dee Dee, and an episode from the series "Copping an Aptitude"; an episode where Dexter had gone to college once.

Box office
The film earned $18.4 million on its opening weekend, followed by $11.7 million on its second weekend, then $12.2 million on its third weekend, after its 45-day period in theaters, the film had grossed 98.1 million; making back its $75 million budget. In other countries, the film had made $52.1 million; with the film having grossed a total of $150.2 million.

Critical response
On review aggregator Rotten Tomatoes, the film has a 76% approval rating of based on 84 reviews and an average rating of 6.72/10. The site's critical consensus reads: "Returned to its roots and paired with a talented new cast, fans of Dexter's Laboratory will find A Boy and His Sister a decent return of Dexter and Dee Dee." Metacritic gave the film a score of 70 out of 100 based on 30 critics, indicating "mixed-or-average reviews". Audiences polled by CinemaScore gave an average grade of "A-" on its A+ to F scale.

Future
A revival of Dexter's Laboratory on HBO Max had been suggested by Shaquille, but will be "shelved" if Tartakovsky has the same interest.