Playwright Mart Crowley appears briefly at the end of the bar in a scene at shot at Julius, a Greenwich Village bar and restaurant that was also shown in the 1970 film.
Boys in the Band was originally an Off-Broadway show, opening in April 1968 at Theatre 4, which was on West 54th Street between 9th and 10th Avenues and running for over two years. The 2018 revival was its first time on Broadway.
In the original play, there are only nine roles: the men who all gather for a birthday party. When the 2018 Broadway production was cast, much of the show's publicity highlighted the fact that all of the actors cast in the play's nine roles are openly gay. This cast was repeated for this film version, so it is again true that the entire main cast is openly gay; however, this adaptation also contains credited actors playing more minor characters who were not present in the play.
One practical filming location was Julius' Bar, a working business that bills itself as New York City's oldest gay bar. It has been in operation as a bar at 159 West 10th Street since 1864, it was a popular speakeasy during the 1920s, and it started to cater predominantly to gay male customers by the 1950s. In 1966 (three years before the more famous protests at the Stonewall Inn, which is around the corner), Julius' was the site of a Mattachine Society protest against the New York State Liquor Authority's discriminatory regulations prohibiting businesses from serving alcoholic beverages to LGBTQ people (which had made it essentially illegal to run or visit a gay bar). The Mattachine Society was one of the earliest American gay rights organizations. The protest, which its organizers dubbed a "Sip-In" (a playful reference to the Sit-Ins of the Southern Civil Rights Movement) was successful; the next year, New York State courts ruled against the State Liquor Authority's practice of revoking the liquor licenses of businesses that served alcohol to LGBTQ patrons. Julius' was also a filming location for the first movie adaptation of Die Harten und die Zarten (1970), the 1970 William Friedkin film.