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.
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 (1960).
The film was shot on location in Rome, Bruges, Stanleyville and a real leper colony 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.
This was one of Audrey Hepburn's favorite of her films. It was also one of her most financially successful.