The Hangover: Part II is a 2011 American comedy film and sequel to 2009's The Hangover. The film stars Bradley Cooper, Ed Helms, and Zach Galifianakis. Justin Bartha and Ken Jeong also reprise their roles. Todd Phillips directed a script written by him, Craig Mazin and Scot Armstrong.

The film was produced by Legendary Pictures and distributed by Warner Bros. Pictures. Production began in October 2010 and was released in the United States on May 26, 2011.

Two years after their escapade in Las Vegas, Stu (Ed Helms), Phil (Bradley Cooper), and Doug (Justin Bartha) are traveling to Thailand to celebrate Stu's wedding to his fiancée, Lauren (Jamie Chung). Not wanting to risk another disastrous experience like the one in Las Vegas, Stu opts to not have a bachelor party, annoying Phil greatly. After much coaxing from Doug, Stu also reluctantly invites Doug's eccentric brother-in-law, Alan (Zach Galifianakis), who has been obsessing over the events from Vegas ever since. The four are also joined, much to Alan's dismay, by Lauren's younger brother, Teddy (Mason Lee), a prodigy who, despite only being 16, is already a pre-medical student at Stanford University. The wedding reception does not go well for Stu, as Lauren's father disapproves of him greatly, considering him boring and being unimpressed that he is a dentist and not a "real doctor"; during his toast, he compares Stu to rice porridge. At night, Phil invites Stu to join the him, Doug, and Alan in having a beer on the beach; Lauren convinces them to bring Teddy along as well to show him a good time. Sitting at a campfire and roasting marshmallows, the group toast to Stu and Lauren's future happiness.

The following morning, Phil, Stu and Alan awaken in a dirty hotel room in an unknown location. Stu has a tattoo on his face and Alan's head is completely shaven. They find that gangster Leslie Chow (Ken Jeong) (whom Alan befriended after Las Vegas) and a chainsmoking capuchin monkey wearing a denim jacket are in the room as well but Teddy is nowhere to be found. Much to their horror, Phil discovers a severed finger with a Stanford class ring attached to it. Chow assures them that nothing bad happened to Teddy but just before he begins recalling the events of the night, he suddenly suffers a heart attack from snorting a line of cocaine and dies. Panicked, the trio dispose of Chow's body in an ice machine on the hotel roof but because the power is out, they are unable to use the elevator and instead have to carry him up the stairs. Upon reaching the roof, they realize that they are in Bangkok. After calling Doug (who left early the last night and is still at the wedding reception), they find out that Teddy was arrested and in jail waiting to be picked up by them. However, the "Teddy" at the prison turns out to be a handicapped elderly Buddhist monk, who is wearing Teddy's sweater. They attempt to ask the monk about Teddy but he has taken a vow of silence and refuses to speak. Discovering a card for a night club in the sweater, the trio travel to that location only to find the entire neighborhood smouldering in ruins. They enter a tattoo parlor next door, where the owner explains that the trio and Teddy had started a fight in the club that escalated into a riot, showing them video footage of the events on his phone. The trio then return the monk to his Buddhist temple, upon which they are beaten repeatedly for speaking without permission. Encouraged by the head monk to meditate to help remember past events, Alan is able to recall a strip club that they had gone to. There, they discover no new leads but do learn that Stu had apparently engaged in sex with a katoey prostitute at the bar (with Stu being on the receiving end). Upon exiting the bar, the trio are attacked by two Russian mobsters from whom they had apparently stolen the monkey and Phil is shot in the arm.

After Phil is treated at a clinic, Alan finally confesses that he had drugged some of the marshmallows from the previous night with muscle relaxants and ADHD medication in order to sedate Teddy but accidentally mixed up the bags and all of them ended up eating some. This causes Stu to snap and attack Alan but through the fight, they notice an address and time point for a meeting written on Alan's stomach. The trio arrive at a luxurious hotel to find another gangster, Kingsley (Paul Giamatti), who tells them that he made a money transfer deal with Chow the previous night and they had agreed to use Teddy as collateral. Kingsley demands that the trio bring him Chow and/or his bank account access code for the money by the next morning if they want to see Teddy alive again. They return to the hotel to try to find if Chow's code is somewhere on his body but discover that he is still alive. Chow explains that he had hidden the code in the monkey's jacket. As a result, the trio and Chow are forced to find the monkey again, who works as a drug trafficking "middleman" for the Russian mobsters. They manage to steal the monkey but barely escape with their lives in a violent car chase, during which the monkey is shot and injured. After taking the code and leaving the monkey at a veterinary clinic, the group return to Kingsley's hotel and transfer the money to him. Suddenly, Interpol agents appear and arrest Chow; Kingsley turns out to be an undercover agent who had invented the entire storyline about Teddy being collateral as a cover to entrap Chow. He tells the trio that the police have searched all day for Teddy but were unable to find him.

Desperate and out of clues, Phil once again calls Doug's wife Tracy to inform her that they have "fucked up." Just as Stu is contemplating living in Bangkok and never returning to the US, the power in the city goes out again. He then has an epiphany and realizes where Teddy has been all along: trapped in the hotel's broken elevator. The trio rush back to the hotel and indeed find Teddy in the elevator unharmed (albeit still missing a finger). Teddy also finds the keys to Chow's speedboat in his pockets and the four use to boat to travel back to the wedding reception. Arriving just as Lauren's father is about to cancel the wedding, Stu makes a defiant speech where he rejects being boring and instead states that he is in fact quite wild with "a little demon inside him." Impressed by Stu's sudden display of authority and confidence, Lauren's father finally accepts him and gives the couple his blessing. After the wedding continues on, Alan presents Stu with a special gift at the post-reception dance: a musical guest performance by Mike Tyson. Later at night as Phil, Stu, Alan, Doug, and Tyson reminisce about all of their crazy escapades, Teddy discovers that he had taken many pictures during the night on his mobile phone. Once again, the group agree to look at the pictures together once before erasing the evidence of their exploits.