Audrey Hepburn met the real Marie-Louise Habets - inspiration for the novel and film - while she was preparing for the role. The two actually became great friends and Habets later nursed Hepburn back to health after her near-fatal horse-riding accident on the set of The Unforgiven.
Fred Zinnemann was strongly opposed to the studio's demand that there should be music over the final scene. Zinnemann felt that music would detract from the depth and grace of Audrey Hepburn's performance in this pivotal scene. Jack L. Warner felt otherwise but eventually relented. The scene remains one of the most memorable and famous from this acclaimed film, precisely for its restraint.
A patient in the Congo hospital has lines in just one scene; when it was necessary to dub over his line, it was spoken by Dean Jagger.
A real priest was cast as Father Andre the chaplain but his acting left much to be desired so Stephen Murray was cast at short notice.
After acquiring the rights to Kathryn Hulme's bestselling novel, Fred Zinnemann found that no one in Hollywood had any enthusiasm towards turning it into a film, citing it as being devoid of action. All that changed when Audrey Hepburn expressed a desire to take the lead role. Suddenly, a bidding war ensued which was won by Warner Brothers and netted them not only one of the most acclaimed films of the year but also their biggest financial hit for 1959.
An often-reported legend surrounding this movie is the story that Audrey Hepburn demanded a bidet be provided for her on location in the Congo. Hepburn always denied this, wondering how such an extravagance could even be hooked up in the Congo.
Members of the Rome Opera ballet corps were hired to play some of the nuns, and complex convent rituals were literally choreographed for them.
The film was based on the novel of the same name, that told the story of the real-life "Sister Luke," Marie-Louise Habets. In the film, Audrey Hepburn's sisters (siblings) were named Marie and Louise.
The film was shot on location in Rome, Bruges, Stanleyville and a real leper colony in the Congo.
The opening credits play out over street scenes of Bruges (or Brugge in Dutch), at over 1,500 years old (though did not receive its city charter until 1128), one of the oldest cities in Belgium, and at one time, the most important commercial city in the world.
The role of Sister Luke was suggested for Ingrid Bergman but Bergman herself said she was too old for the role and instead proposed Audrey Hepburn.
The scenes where this is palpable sexual tension between Dr Fortunati and Sister Luke are not present in the novel.
This was one of Audrey Hepburn's favorite of her films. It was also one of her most financially successful.