The group of friends are based on the director's real childhood friends.
Based on the break off and war between the 7 star and 20th Century mob families in Busan.
In-Pyo Cha turned down the lead role.
Upon the film's 2001 release in South Korea, it became the highest grossing film of an 18+ rating with 8.1 million audiences within two months. It held the record for 14 years, when in 2015 the movie "Inside Men" became the new highest grossing 18+ film with 9.1 million audiences. Filmmakers Park Chan Wook and Bong Joon Ho have stated that for its time, 8.1 million is an impressing number, which is equivalent to about 17 million in 2020.
The entirety of the film's dialogue between the main characters consist of the Busan dialect, in which the intonation is very different from the standard Seoul dialect. Actors Seo Tae Hwa and Jeong Un Taek are native speakers of the Busan dialect, while Yu Oh Seong and Jang Dong Gun aren't. They had to receive separate lessons from an accent coach on perfecting the Busan intonation, but at the time of its release native Busan residents claimed that the actors' accents were still a tad awkward.