Set in Saigon in 1965, during the Vietnam War, the film stars Robin Williams as a radio DJ on Armed Forces Radio Service, who proves hugely popular with the troops, but infuriates his superiors with what they call his "irreverent tendency". The story is loosely based on the experiences of AFRS radio DJ Adrian Cronauer. 
Most of Williams' radio broadcasts were improvised. The film was a critical and commercial success; for his work in the film, Williams won a Golden Globe Award for Best Actor – Motion Picture Musical or Comedy and was nominated for an Academy Award for Best Actor, a BAFTA Award for Best Actor in a Leading Role. The film is number 100 on the list of the " American Film Institute's 100 Funniest American Movies ".
In 1965, Adrian Cronauer arrives in Saigon to work as a DJ for Armed Forces Radio Service. Cronauer is met at the airport by PFC Edward Garlick. Cronauer's attitude and demeanor contrasts sharply with many staff members. His show consists of irreverent humor segments and rock and roll, which are frowned upon by his superiors, Second Lieutenant Steven Hauk and Sergeant Major Phillip Dickerson. Hauk adheres to strict Army guidelines in terms of humor and music programming, while Dickerson is generally abusive to all enlisted men. However, Brigadier General Taylor and the other DJs quickly grow to like the new man and his brand of comedy.
Cronauer meets Trinh, a Vietnamese girl, and follows her to an English class. Bribing the teacher to let him take over, Cronauer instructs the students in American slang. Once class is dismissed, he tries to talk to Trinh but is stopped by her brother Tuan. Instead, Cronauer takes Tuan to Jimmy Wah's, a local GI bar, to have drinks with Garlick and the station staff. Two soldiers, angered at Tuan's presence, initiate a confrontation that escalates into a brawl.
Dickerson reprimands Cronauer for this incident, but his broadcasts continue. While relaxing in Jimmy Wah's one afternoon, he is pulled outside by Tuan, who says that Trinh wants to see him. Moments later, the building explodes, killing two soldiers and leaving Cronauer shaken. The cause of the explosion is determined to be a bomb; the news is censored, but Cronauer locks himself in the studio and reports it anyway. Dickerson cuts off the broadcast and Cronauer is suspended. Hauk takes over his shows, but his corny humor and the polka music he plays lead to a flood of letters and phone calls demanding that Cronauer be put back on the air.
In the meantime, Cronauer spends his time drinking and pursuing Trinh, only to be repeatedly rebuffed. At the radio station, Taylor intervenes on Cronauer's behalf, ordering Hauk to reinstate him, but Cronauer refuses to go back to work. Garlick and Cronauer's vehicle is stopped in a congested street amidst a convoy of soldiers from the 1st Infantry Division, who persuade him to do an impromptu "broadcast" before they go off to fight. The incident reminds him why his job is important, and he soon returns to the air.
Dickerson seizes an opportunity to get rid of Cronauer by approving his request to interview soldiers in the field, knowing that the highway to An Lộc is controlled by the Viet Cong. Cronauer and Garlick's Jeep hits a mine and they are forced to hide from VC patrols. In Saigon, Tuan learns of the trip after Cronauer fails to show up for English class. He steals a van and drives off after them. After finding them, the van breaks down and they flag down a Marine helicopter to take them back to the city.
At the station, Dickerson tells Cronauer that he is off the air for good. His friend Tuan is revealed as a VC operative who was responsible for the bombing of Jimmy Wah's. Dickerson has arranged for an honorable discharge. General Taylor arrives and informs Cronauer that, regrettably, he cannot help him since his friendship with Tuan would damage the reputation of the US Army. After Cronauer leaves, Taylor informs Dickerson that he is transferring him to Guam, citing Dickerson's vindictive attitude as the reason.
Cronauer chases down Tuan, decrying his actions against American soldiers. Emerging from the shadows, Tuan retorts that the US army has devastated his family, and for him that makes the United States the enemy. On his way to the airport with Garlick, under MP escort, Cronauer sets up a quick softball game for the students from his English class, where he says goodbye to Trinh. As he boards the plane, he gives Garlick a taped farewell message; Garlick – taking Cronauer's place as DJ – plays the tape on the air the next morning.
- Robin Williams as Airman Second Class Adrian Cronauer
- Forest Whitaker as Private First Class Edward Montesquieu "Eddie" Garlick
- Tung Thanh Tran as Tuan / Phan Đức Tô
- Chintara Sukapatana as Trinh
- Bruno Kirby as Second Lieutenant Steven Hauk
- Robert Wuhl as Staff Sergeant Marty Lee Dreiwitz
- J. T. Walsh as Sergeant Major Phillip Dickerson
- Noble Willingham as Brigadier General Taylor
- Richard Edson as Private Abersold
- Richard Portnow as Sergeant Dan "The Man" Levitan
- Floyd Vivino as Eddie Kirk
- Juney Smith as Sergeant Phil McPherson
- Củ Bà Nguyễn as Jimmy Wah
- Dan R. Stanton as Censor #1
- Don E. Stanton as Censor #2
- Ralph Tabakin as Chaplain Captain Noel
In 1979, Adrian Cronauer pitched a sitcom based on his experiences as an AFRS DJ. TV networks were not interested, however, because they did not see war as comedy material,  even though one of the most popular shows at the time was M*A*S*H . Cronauer then revamped his sitcom into a script for a TV movie of the week, which eventually got the attention of Robin Williams.  Very little of Cronauer's original treatment remained after writer Mitch Markowitz was brought in. 
According to Cronauer, he and Williams were forbidden by Levinson to meet each other because the director "was afraid that if Robin and I met, that Robin would somehow start to do an unconscious imitation of me, which would change his characterization." Williams and Cronauer eventually met at the film's New York premiere. 
Good Morning, Vietnam was one of the most successful films of the year, becoming the fourth highest-grossing film of 1987.
The film received outstanding reviews from film critics. The website Rotten Tomatoes, which compiles critical reviews for movies, gave a rating of 90%  and the consensus: "A well-calibrated blend of manic comedy and poignant drama, Good Morning, Vietnam offers a captivating look at a wide range of Robin Williams' cinematic gifts." Both Roger Ebert and Gene Siskel of the review show Siskel and Ebert awarded the film "Two Thumbs Up", with Ebert giving the film a four out of four star review in the Chicago Sun-Times .  Richard Corliss of Time called the film "the best military comedy since M*A*S*H ", and named it one of the best films of the year. Vincent Canby of the New York Times called the film a cinematic "tour de force" and described Williams' performance as "the work of an accomplished actor". Much of the acclaim went to Williams' performance, a role that earned him an Oscar nomination for Best Actor. 
Awards and honors
- Robin Williams won a Golden Globe Award for Best Performance by an Actor in a Motion Picture - Comedy/Musical, and an American Comedy Award for Funniest Actor in a Motion Picture (Leading Role). He was also nominated for a Best Actor Academy Award, a Best Actor BAFTA Award, and a Sant Jordi Award for Best Foreign Actor. 
- Forest Whitaker was awarded a Sant Jordi Award for Best Foreign Actor for his work on this film and Bird . 
- Alex North was awarded the ASCAP Award for the film's original music. 
- The film won the Political Film Society Award for Peace, and was nominated for a Best Sound BAFTA Award. 
- AMC named Good Morning, Vietnam one of the 20 greatest war movies of all time. 
- In 2000, American Film Institute included the film in AFI's 100 Years...100 Laughs (#100). 
The soundtrack album was certified platinum in the US. Louis Armstrong's "What A Wonderful World" was released as a single because of the film and reached position 32 on the US Top 40, 20 years after its original release.