The film begins and ends with a wedding. As the picture opens, three couples are leaving a church where a friend's daughter has just been married. The three men are business partners: Ricardo, Raúl and Arturo. Ricardo is married to Adriana; they have a 19-year-old daughter (Marta), and two young sons; Arturo is married to Elena, but has a roving eye; Raúl and Hilda are not married, but have a long-standing romantic relationship (Hilda is divorced from an alcoholic and has a daughter, Andrea).

Most of the plot revolves around Marta and her law-student boyfriend, Rubén. Marta is three months' pregnant with their child, but the couple has not told their parents. They want to get married, but know Ricardo will oppose the match. Rubén tells his father, but he and Marta can never find the right moment to inform the irascible Ricardo. When Marta falls ill with an infection, she reveals the truth to her mother, with the aid of kindly Dr. Aponte. However, the only way they can break the news to Ricardo is to pretend Marta is at death's door; Ricardo, shocked by the news, topples into a bookcase and is hit on the head with a vase. Rubén trips on a rollerskate and breaks his leg. However, the wedding goes off as scheduled, but Marta doesn't make it to the reception, since she goes into labor and has to be taken right to a hospital where she gives birth.

The film includes several other sub-plots. One of these involves Hilda's relationship with her daughter, Andrea. Andrea, although she will not openly say so, is ashamed of her mother's "free love" with Raúl. She rebels by engaging in inappropriate (for the time) behavior with her playboy boyfriend Carlos. Hilda, while she is theoretically opposed to marrying just for the sake of propriety, is worried that Andrea will see only the scandalous aspects of her life with Raúl. Other, minor sub-plots feature the sexy Samanta, daughter of Ramón, an old school friend of Arturo. Arturo and Raúl encourage her to to say in Mexico and not go back to New York to marry her fiance. Raúl is hired by a blonde gringa to be her divorce lawyer.

The latter thread provides most of Mauricio Garcés' amusing moments in the film. Bárbara (Amedee Chabot--dubbed with a deeper voice than usual) enters Raúl's office, but her dress gets caught on the door and ripped off, leaving her standing there in her underwear. "If this is a trick to get me to reduce my fees--I'll do it!" Raúl says. He talks to her in broken English: "Don't you want a little cognac-ito?. . . Please put your beautiful seat on the chair . . . " Bárbara says she wants a divorce from her insanely jealous husband. Raúl agrees to take the case ("From now on you have your own Latin lover") but reminds his secretary (in Spanish): "I'm not in to anyone, and if it's a gringo, I'm out of the country."

Later, Bárbara visits Raúl at his house and says she is now a rich widow, her husband having died suddenly. They play gin rummy, using her inheritance as stakes, but Bárbara wins easily (this is a funny sequence, without dialogue, as Garcés watches Chabot very carefully with each card that is played). Socrates, Raúl's major-domo, tells Raúl that Bárbara's husband was from Chicago and died in Las Vegas: "Get this gangster out of here!" Raúl orders.

Aside from these and few other mildly amusing scenes, El día de la boda is only fair entertainment and largely a waste of a dynamite cast.