It's set in Naples. Domenico (Mastroianni) is a wealthy 50-year-old businessman, engaged to be married to a shopgirl in one of his stores, who is less than half his age. Domenico is in the middle of making wedding plans when he receives word that Filomena, his mistress/Girl Friday of 22 years, is dying. He rushes to her bedside and, before Domenico even knows what is happening, they are married.
Domenico thinks that he has fulfilled his mistress's dying wish, and is pretty pissed off when he finds out that Filomena wasn't sick at all and the whole business was a trick to get him to marry her. Filomena for her part is unapologetic, believing marriage is her due as his longtime companion. While all these complications play out, Domenico and Filomena's two-decade relationship unspools in a series of flashbacks.
One of 13 films co-starring Loren and Mastroianni and one of 16 films where Loren either co-starred with or was directed by De Sica.
- Call-Back: When we first see Filomena's second son as a boy, he's eating a powdered sugar doughnut and making a mess of it. Ten years later or so, he's eating another powdered sugar doughnut, and making a mess of it again.
- Confirmed Bachelor: Domenico is your typical louche Italian bachelor, keeping a long-term mistress, unashamed about bringing home a bunch of porn magazines from a trip. It's when he finally decides to get married but not to Filomena that she's driven to take radical action.
- Fanservice: Is there a scene with Sophia Loren in revealing lingerie as Filomena is working in a brothel? Why yes, yes there is.
- Fanservice Extra: Two different scenes in brothels filled with attractive prostitutes. Then there's the woman in Domenico's office modeling lingerie.
- Flashback: Many, as the present-day story of Filomena and Domenico's marriage is periodically interrupted by flashbacks telling their backstory.
- Gilligan Cut: The servants, worried about having to tell Domenico that Filomena is dying, say "What a shock for him." Cut to Domenico kissing his young, sexy fiancee.
- High-Class Call Girl: Filomena's regular job, and one she apparently continues to work at for quite a while when she isn't with Domenico or managing Domenico's businesses in his absence.
- The Joy of X: One of the first films to follow in the wake of Divorce Italian Style (1961), which also happened to star Marcello Mastroianni.
- Luke, I Am Your Father: Filomena farmed out her three children to the country while she worked as a prostitute in Naples. Eventually she calls them all to Rome, assembles them together (they were raised separately), and informs them that they are brothers and she is their mother.
- Mama's Baby, Papa's Maybe: Filomena eventually reveals that she has three children, a fact she has kept from Domenico for a full twenty years (the oldest is a university student). She says that one of them is his but refuses to say which.
- Mistaken for Gay: Domenico is obsessed with finding out which of Filomena's sons is his. He goes to the shoe store where one son works. His leading questions, ending with "You like girls, do you?" (Domenico is looking for a fellow Casanova), leads the young man to draw the entirely wrong conclusion.
- The Mistress: Filomena for over two decades, although for at least part of that time she was still hooking while Domenico was away. She eventually grows tired of this subordinate role in his life.
- Meet Cute: They meet for the first time when Domenico, who has to get out of a brothel due to an Allied bombing raid, discovers a frightened Filomena hiding in a closet.
- Never Learned to Read: Domenico finds this out when Filomena slowly, laboriously scrawls her signature on the deed to an apartment. And she never does learn, even after years running his business.
- Romantic Rain: Filomena and Domenico's second meeting, after the Americans have liberated Naples, involves Domenico running into her by chance and giving her a ride in his car. Rain forces Domenico to stop driving. Sex follows.
- Slap-Slap-Kiss: An angry confrontation between Filomena and Domenico on the slopes of Mount Vesuvius leads to both of them stumbling off the side of the road and into a ditch. Domenico lands on top of her and starts yelling at her. Kissing and an emotional reconciliation follows.
- Toplessness from the Back: A little more fanservice from Filomena.
- Unwanted Spouse: Domenico immediately takes action to get an annulment after finding out what Filomena did.