Secret Ceremony is a 1968 British psychological thriller film directed by Joseph Losey and starring Elizabeth Taylor, Mia Farrow and Robert Mitchum. Based on the 1960 novel Ceremonia secreta by Argentine author Marco Denevi, the film follows an indigent prostitute who meets a strange young girl who insists that she is her long-lost mother.

While on a bus in London, Leonora, an ageing prostitute, is approached by a waiflike young woman, Cenci, who utters the word "mummy". Cenci follows Leonora to a cemetery where the latter stops to mourn her daughter, who drowned five years earlier at the age of 10. Leonora is taken aback by Cenci's resemblance to her deceased daughter, and hesitantly agrees to accompany the girl to her opulent mansion, where she lives alone. Leonora soon finds that she bears a striking resemblance to Cenci's late mother, Margaret. Although initially unsettled by Cenci's childlike behaviour and need for affection, Leonora agrees to live with her as her surrogate mother.

Leonora hides when Cenci's aunts Hannah and Hilda unexpectedly visit the mansion. The aunts antagonise Cenci while surreptitiously stealing valuable objects, which is witnessed by Leonora. The next day, Leonora visits Hannah and Hilda at their antique shop, lying that she is Margaret's cousin. The aunts tell Leonora that Cenci took care of Margaret through her illness with no help, and that she refused to accept her mother's death. They also reveal that Cenci is 22 years old, despite looking and acting much younger, and that Margaret threw out Cenci's stepfather, Albert, after catching him trying to seduce Cenci. Leonora admonishes the aunts for failing to protect Cenci and warns them to stay away from the mansion.

While alone in the mansion, Cenci is visited by Albert. After she trims his beard, he asks her to make the moaning sounds she made while they had sex; she refuses but eventually obliges, leading Albert to kiss Cenci. Leonora returns to the mansion to find a shaken Cenci cowering under a sink, and Cenci mentions Albert's visit. Leonora and Cenci later check into a luxurious seaside hotel. That night, when Cenci arrives at the dining room sporting a fake baby bump, Leonora is stunned but plays along with the ruse.

The next morning, Albert arrives and confronts Leonora on the beach, declaring that Cenci is mentally unstable and had repeatedly tried to seduce him. Back in their hotel room, Cenci begins to kiss Leonora's back while giving her a back massage, before Leonora angrily tells Cenci to stop. Leonora then forces Cenci to face reality by ripping off her fake baby bump, sending Cenci into a frenzy. Later, from her balcony, Leonora witnesses Cenci and Albert having sex on the beach. When Cenci returns, she sends Leonora away, no longer seeing her as her mother.

Back in London, Cenci overdoses on pills, intending to commit suicide. Shortly afterwards, Leonora visits Cenci and begs to be allowed to stay in the mansion, but Cenci rebuffs her once again. As Leonora leaves, Cenci collapses to her death. Standing beside Albert in silence at Cenci's funeral, Leonora pulls out a knife and stabs him to death. Lying on her bed, Leonora listlessly hits the cord of a ceiling lamp while reciting a nursery rhyme about perseverance.

The short story on which the film is based won a $5,000 prize in a competition run by Life en Español. It had already been filmed for Argentine television when it was optioned in 1963 by Dore Schary.

In an October 1969 interview with Roger Ebert, Mitchum claimed that the film's production was "in trouble" when he arrived and that his presence did not help.