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"The Stockholm Syndrome" is the series finale of the American television sitcom The Big Bang Theory. It is the twenty-fourth episode of the twelfth season and the 279th overall episode of the series. Written by series co-creators Chuck Lorre and Bill Prady, with Steve Holland, Steven Molaro, Dave Goetsch, Eric Kaplan, Maria Ferrari, Andy Gordon, Anthony Del Broccolo, Tara Hernandez, Jeremy Howe and Adam Faberman. The episode was directed by Mark Cendrowski. The episode originally aired on CBS on May 16, 2019 in the United States. The episode finds Sheldon and Amy receiving a Nobel Prize in Physics, and Penny reveals she is pregnant. Sarah Michelle Gellar guest stars as herself. The Stockholm Syndrome was watched by 24.75 million total viewers in the United States and garnered positive reviews from critics.

After Sheldon and Leonard spend two months repairing Sheldon's DNA molecule model, everyone prepares to fly to Sweden for the Nobel Prize award ceremony. Howard and Bernadette nervously leave their kids for the first time with Stuart and Denise, while Raj leaves his dog Cinnamon with Bert. Penny and Leonard are continuing to keep Penny's pregnancy a secret.

Traveling outbound, the group cram all their luggage in the now-working elevator in their apartment building and are forced to take the stairs themselves. On the flight, Raj is seated next to a sleeping , but his friends do not believe it is her. Penny's frequent bathroom trips make Sheldon fear she is sick. Penny reveals her pregnancy to Sheldon but, instead of being excited for her, Sheldon is only relieved that she is not contagious and reveals the pregnancy to everyone on the plane. Leonard is upset that Sheldon is not happy for them, and Amy and Bernadette are both annoyed at Penny that they did not find out about the pregnancy from her.

Steve Holland said that the writers were aware of fan expectations about the finale, but aimed to write what "felt right" to them—in particular, the idea that there was a "big emotional climax" after which the characters would "get up and go to work together", with their lives continuing as normal.

Guest star Sarah Michelle Gellar came to fame as the eponymous Buffy in Buffy the Vampire Slayer. The program has been referenced by The Big Bang Theory previously, and writers Steve Molaro and Holland were fans. When the writers realized that Raj would not be seated next to anybody on the plane, Chuck Lorre suggested it would be a good opportunity for a celebrity guest star. Before Gellar was cast, Sandra Bullock was offered the role, but politely declined due to scheduling conflicts.

The characters' clothing evokes the pilot, while Leonard and Sheldon take 139 hours 30 minutes to rebuild the DNA molecule, which is the total length of time of The Big Bang Theory (with each episode running 30 minutes with commercials).

"The Stockholm Syndrome" was first broadcast on CBS on May 16, 2019, at 8 p.m., and was watched by 18.52 million viewers on CBS, the highest viewing figure that night, and ranking #1 for the day. It received a 3.2 rating and a 17 share in the 18–49 demographic, and aired at 8 p.m. alongside Grey's Anatomy on ABC, Superstore on NBC, Paradise Hotel on Fox and iZombie on The CW.

In Canada, the episode received 4.33 million viewers on CTV, making it the most watched episode that year. In Australia, the episode aired on the Nine Network on July 3, 2019, and had 1 million viewers.

Daniel Fienberg from The Hollywood Reporter gave the episode a positive review, writing that the show had matured through "strong, funny female characters" since its unkind and crude first episode. Fienberg found Sheldon's acceptance speech moving and enjoyed the final scene. However, he criticized that the finale "didn't know what to do with Raj", that it did not sufficiently explore Penny's changed mind over having children, and that Sheldon's speech had ambiguities of being "a dream or hallucination".

Saloni Gajjar from Mashable summarized the episode as "sweet, tying up everything with a formulaic sitcom-style ending". Gajjar saw Amy's speech as one of a few "rare moments" in the show that "let shine the importance of women in science", found the working elevator to be the most surprising development in the episode, and criticized that Raj's narrative lacked closure and Penny's "sharp turn" to wanting children was undeveloped.

Brian Lowry from CNN wrote that "The Stockholm Syndrome", along with the previous episode, "felt satisfying and appropriate, if somewhat low-key". He said that it reflected how the show developed, through the addition of "key female characters" and "more grown-up problems and issues", without abandoning the focus for nerdy topics.