The film's $6 million budget was supplied by three different sources: $2 million from United Artists, $2 million from Paramount and $2 million from 20th Century Fox.
Bernardo Bertolucci stated that in an interview, he filmed the scenes of the movie based on the four seasons. If you notice, the meeting of the boys is summer, the adult reunion of Alfredo and Olmo takes place in a fall moment. The Fascist takeover is winter, while the end of World War Two is spring.
Original uncut version is 5.5 hours long, and features explicit sex scenes with Alfredo, Olmo, and Neve. It also featured prepubescent boys examining each other's penises.
The integral version of the film, the entire 5 hours and 20 minutes, was shown for the first time in 30 years in Belgrade, Serbia (ex-Yugoslavia), on April 12 2007.
The painting shown during the opening credits is Giuseppe Pellizza da Volpedo's "Il quarto stato" (1901).
Bertolucci himself cut the 3.5 hour version that was originally shown internationally, which he did to appease the studios and financiers, who wanted to use an even shorter cut that was never released. He still says he prefers the original 5 and half hour cut. His main complaint with the international release was the English title "1900". With the original title "Novecento", he meant to imply a tale of the 20th century.
The full uncut version (315 minutes) is available in DVD since late 2006 (two discs) including some interviews with Bertolucci.
More than 12,000 extras were employed.
Donald Sutherland got so upset after seeing his own performance as the sadistic homicidal fascist leader Atilla, that he was unable to watch the film for years.