Teenage Mutant Ninja Turtles is the 1990 live-action film based on the Teenage Mutant Ninja Turtles franchise. The film was followed by three sequels, Teenage Mutant Ninja Turtles II: The Secret of the Ooze, Teenage Mutant Ninja Turtles III and TMNT. This film presents the origin story of Splinter and the Turtles, the initial meeting between them, April O'Neil and Casey Jones, and their first confrontation with Shredder and his Foot Clan. The film's core plot closely follows that of the first published TMNT story, from Teenage Mutant Ninja Turtles #1.

When the NYPD is unable to stop a severe crime wave caused by the Foot Clan, four new vigilantes, Leonardo, Michelangelo, Donatello and Raphael, will come forth to save the city. Under the leadership of Splinter and together with their new-found allies April O'Neil and Casey Jones, they will fight back and take the battle to Shredder.

The film kept very close to the dark feel of the original comics with only few elements making it in from the cartoon. The film received positive reviews, was the highest-grossing independent film of all time when it was released, a huge hit at the box office, and became the fifth highest grossing film worldwide of 1990.

As the film begins April O'Neil, an investigative reporter at Channel 3 Eyewitness News, is researching a story on a recent, immense crime wave in New York City. Meanwhile, ex-hockey player Casey Jones decides to become a vigilante so as to combat the crime wave. He is shown beating two thieves with his sports equipment and arguing with the Teenage Mutant Ninja Turtle Raphael over the proper way to punish criminals. The crime wave is traced by April to the Foot Clan; when she makes them uncomfortable, the Foot Ninjas attack her. Raphael rescues her.

As the Turtles escort April back to her apartment, the Foot find the Turtles' lair and kidnap Splinter. They carry him back to their headquarters, where their master Shredder is forming an army of corrupted, ninja-trained teenagers to build himself an empire of crime. One of those teenagers is the son of April's boss; having seen the Turtles at her apartment, he tells Shredder where to find the Turtles. The Foot launch a surprise attack on April's apartment. Caught off-guard and outnumbered, April, the Turtles, and Casey (who had intervened when he saw Raphael in danger) are forced to escape to April's childhood home in the country. Raphael is rendered unconscious during the battle and does not wake from his coma for several days.

After Raphael's recovery from his coma, the Turtles refine their ninja skills in anticipation of their return to the city. They return to New York and fight the Foot while Casey rescues Splinter. The Turtles take the battle to the sewers, to the streets, and ultimately the rooftops, where they meet the Shredder. The Shredder proves to be an enemy of skill outstripping their own; however, his victory is forestalled when Splinter unexpectedly arrives. Splinter reveals that the Shredder is Oroku Saki, the man who killed his beloved master Hamato Yoshi. The Shredder is then reminded of a much-resented scar inflicted on him by Splinter. When the Shredder tries to impale him, Splinter calmly uses Michaelangelo's nunchaku to grab his attacker's spear and flip Shredder over the side of the building. With the spear stuck in the nunchaku, the Shredder throws a knife at Splinter, but Splinter catches it. This causes Splinter to release the nunchaku and Shredder to fall off of the roof of the building and into a garbage truck. Casey activates the crushing mechanism, whereupon Shredder is apparently crushed to death.

The trainees of the Foot Clan confess all of their involvement to the New York Police Department, while Casey kisses April. The film concludes with Partners In Kryme's track "T-U-R-T-L-E Power" and the Turtles celebrating their victory over the Foot Clan.

The film was well received by fans, and did exceedingly well at the box office. Reviews were for the most part positive. However, Roger Ebert gave it only 2 and a half stars, saying, "But this movie is nowhere near as bad as it might have been, and probably is the best possible Teenage Mutant Ninja Turtle movie. It supplies, in other words, more or less what Turtle fans will expect." The film was also somewhat looked down upon for its level of violence, but it was mostly stylized and not graphic. The film was praised for the most part staying very loyal to the original comics, and not integrating too many elements from the cartoon series. Despite getting "two thumbs down" on the television show Siskel & Ebert, the film remains a favorite among Ninja Turtles fans.

The film opened at the box office in North America on March 30, 1990. It opened at #1 over the weekend, taking in more than $25 million. The film turned out to be a huge success at the box office, eventually making over $135 million in North America, and over $66 million outside North America for a worldwide total of over $200 million, making it the fifth highest grossing film of 1990 worldwide. The film was also nominated for Best Costumes and Best Fantasy Film at the 1991 Saturn Awards, as well as the Most Entertaining Family Youth Motion Picture - Drama at the Young Artist Awards.

Following the huge success of Teenage Mutant Ninja Turtles at the box office, several sequels were created. Only a year later, Teenage Mutant Ninja Turtles II: The Secret of the Ooze was released in theatres, and in 1993 Teenage Mutant Ninja Turtles III was released in theatres. Both films were successful at the box office (though they where less well-received than the first film), but it is generally thought that the first installment of the series was the best, due to it keeping itself closely aligned to the original comic book. After a number of years absence from the theatres, a fourth film was released in 2007, though unlike the first three, this is a CGI animated film.

Filming took place from July to September of 1989. The film's budget was $13.5 million. A lot of the production took place in North Carolina, at the North Carolina Film Studios, where New York rooftop sets were created. Production designer Roy Forge Smith and his art director, Gary Wissner, went to New York City four months prior to filming and took still photographs of rooftops and other various locations. While in NYC, Smith and Rissner were allowed to explore an abandoned Brooklyn subway line, as they could not gain access to a city sewer, but the structure of the subway had the same principle as a sewer. They also went to a water tunnel which had large pipes running through it.

After design sketches were created, the construction team used the studios' backlot to create some of the sets. There were problems with the manholes that led to the Turtles' home, in that an eight-foot square room had to be constructed beneath them, but found water at about five-feet, and thus had to pour concrete into the underground rooms to keep the water out. In order to make the sewer authentic, a tide-mark was given, and it was covered with brick, plaster and stucco paint to give the walls a realistic look. The Turtles' themselves were done by Jim Henson's Creature Shop in London. Jim Henson said that the creatures were the most advanced that he had ever worked with. The creatures were first made out of clay, which were then rebuilt out of fibre glass. They were produced as moulds to cast the whole body in foam rubber latex. Work was then done on mechanizing the fiberglass. The work at the Shop was completed within 18 weeks.

There have been many alleged deleted scenes in this movie. While some are simply rumors, others are seen in the Archie comic adaptation of the movie or found in early versions of the script. Also, the Summer 1990 issue of TMNT Magazine features a number of publicity shots for the movie, some of which depicting scenes that do not occur in the movie, and the Teenage Mutant Ninja Turtles: The Movie Sticker Album released by Diamond the same year also includes references to some deleted scenes. The Topps trading card series also has numerous pictures of deleted, alternate and publicity like scenes. The trailer for the movie which is included on the DVD shows four specific scenes or shots cut from the final film.

The UK release of the film was, for the time, heavily edited to remove many references to nunchaku as a weapon, due to political concerns at the release relating to a rise in violence involving them as a weapon at this time. As a result, one scene (in which Michaelangelo and a Foot ninja display their prowess with the weapons) was cut entirely, and the ending in which Splinter wields a pair of nunchaku was heavily edited. In 2003, prior to DVD release, the film was resubmitted to the BBFC and passed without cuts, restoring all edits made for the original releases.

According to some rumors, Steve Barron found an earlier cut of the movie. That cut didn’t have music or sound effects added yet, and the voices of the puppeteers performing the turtles' heads can be heard over the voice actors. It also included several scenes that are not in the finished movie, including:

An alternate ending, where an unemployed April has decided to take the concept of the TMNT to a comic book publisher. April and Danny are shown waiting anxiously in the publisher’s office, as the publisher perused her sketches and proposal. Finally, he hands them back to her, saying "The idea is too far-fetched." Hearing that, the Turtles, who had been clinging to the wall outside the office window, react with various expressions of comic dismay, and Michelangelo actually falls off the building. The comic book publisher’s office is decorated with fake comic book covers featuring characters from Mirage Studios, which Mirage has provided. This alternate ending was included in the movie's novelization.

An introduction scene for Casey Jones. It shows Jones in his apartment, watching the news about the recent crime wave. He gets mad and grabs his hockey mask off a table. The same scene was used to introduce Jones in the 2003 cartoon episode Meet Casey Jones.

An extended training scene on the farm. This scene was part of the theatrical release, and only deleted from the video release. After Leonardo hears Splinter's voice through meditation, he challenges his brothers to attack him while blindfolded by his own mask, and proceeds to fend off each of their attacks. There is poster of Donatello wearing a straw hat and chewing on a piece of straw while leaning against a fence on the farm; this scene is not the video. In addition, some recall more character development scenes on the farm in the theatrical version, showing how everyone deals with the situation in their own way, although the video release does show at least some of this, as told by April while writing a journal entry.

Topps cards shows an underground shot of April climbing up after just meeting the Turtles, with Leo close by, a shot of Leo pulling the cover over the manhole before going in Aprils apartment, Leo battling the foot by himself in the antique part of April's apartment, Don standing by himself in a field on the farm, two shots of Don during the training sequence, and one of Raph fighting a Foot during the sewer battle. As posted above the card series includes many alternate shots during fight scenes and many publicity type photos.

The trailer shows two shells coming out of the river, the full scene would show April walking across the bridge to the parking lot, then the shells come up. (For some reason IMDB credits this scene as one of the Turtles coming out of a swamp.) The second scene is of a manhole rumbling then popping off as steam comes out. The camera then zooms into the sewer. The third is of Mike and Don showing off another dance move. And the fourth is of Raph punching two Foot Ninjas in a high outward motion.

Another deleted scene featured an extended scene of the Shredder in which he beats and scars several of the Foot soldiers that had been bailed out of jail and then comments that their scars will remind them of their failure. This was left in the novelization, Mirage's comic book adaptation, and Teenage Mutant Ninja Turtles: The Movie Sticker Album.

The character Shinsho that was beaten by Tatsu originally was supposed to die from the beating. This was deemed too violent and so sounds of Shinsho moaning and the line "You're going to be okay" was hastily ADRed in to imply that he lives. His death remained in the novelization.

The film has been released on DVD in Region 1, though a special edition has not yet been made. Laird and Barron have expressed interest in releasing a "special edition" version of the first movie, with new scenes and other bonus materials. However, New Line Cinema has never commented on this possibility. However, at present there is no special edition release of the film, with the DVD release including only features such as a trailer and interactive menus. Teenage Mutant Ninja Turtles is also available in a three-set package with the other two films that were made in the 1990s.