Set in the slums of Tondo, Manila, the film stars Hilda Koronel as the eponymous character: the young daughter of a resentful mother (Mona Lisa), whose much-younger lover (Ruel Vernal) rapes her.

Unable to get over this rejection, Tonya takes it out on Insiang, treating her miserably and preventing her from pursuing relationships with men.

Insiang's car-mechanic boyfriend Bebot sneaks into her house one night and asks her to have sex to make up for missing their date.

He admits to having sex with Insiang, but convinces Tonya that her daughter tried to seduce him by bathing (and lying nude) in his presence.

She finds Bebot acting cold and distant the following day; that night, Insiang asks Dado to avenge her.

I wanted to show the violence of the overcrowded neighborhoods; the loss of human dignity caused by the social environment and the ensuing need for change.

[14][16] Policemen were on duty during the shoot to prevent the crew from being bothered by gangsters, since the slums of Tondo had an organized-crime presence.

Marcos's wife Imelda was critical of the film, saying that it barely depicted a "beautiful view" of the Philippines,[17] and it was a target of censorship by governing bodies for the same reason.

[16] Imee Marcos, however, was a principal sponsor to the film's fundraising premiere, with proceeds going to the squatter outreach program of Assumption College San Lorenzo and the burn unit of the Philippine General Hospital.

[9] It was unsuccessful at the Philippine box office, forcing Brocka's production company (CineManila Corporation) into bankruptcy.

[16] Tiong Tan, Koronel and Brocka traveled to France for the festival, the producer reportedly smuggling the film rolls in her luggage to prevent customs officers from confiscating them; she had added English subtitles.

[20] In 2015, Insiang was digitally restored in a joint effort by the World Cinema Project (owned by director Martin Scorsese), L'Immagine Ritrovata and the Film Development Council of the Philippines (FDCP).

The three organizations were also involved in the 2013 restoration of Manila in the Claws of Light (Maynila, sa mga Kuko ng Liwanag), a film directed by Brocka in 1974.

[2] Insiang received good reviews from foreign and domestic critics,[18] some of whom called it Lino Brocka's masterpiece.

[3][1][22][28] Richard Brody of The New Yorker called it an "intense, furious melodrama" which "fuses its narrative energy with documentary veracity".

[24] Manohla Dargis of The New York Times wrote "Throughout, Mr. Brocka, working with his excellent director of photography, Conrado Baltazar, creates images of startling power, like that of bloody hands clutching in the void.

"[11] Nick Schager of Slant Magazine gave the film a score of 3.5 out of 4: "Brocka's portrait of familial treachery and societal abandonment channels its melodrama through the filter of neorealism, its story's heightened emotions kept at a simmer by an aesthetic at once verité-blunt and yet shrewdly, meticulously composed.

"[20] Michael Joshua Rowin of Reverse Shot (a Museum of the Moving Image publication) was, however, critical of its status as a masterpiece: "Insiang is all skeleton and little flesh: the actors trudge in front of the camera, woodenly recite the purely functional lines from Lamberto E. Antonio and Maria O'Hara's screenplay, and wait for Brocka to provide some sort of commentary.