Mayil is a 16-year-old schoolgirl who lives in a village with her mother, Guruvammal. Guruvammal also takes care of the limping orphan Gopalakrishnan, who is called "Chappani" ("Lame") by the villagers and does whatever he can to earn a living. Mayil's ambition is to become a teacher, and she hopes to marry a sophisticated, educated man; although Chappani is in love with her, she ignores him.

An urban veterinarian named Sathyajith arrives in the village to work and falls in love with Mayil. Believing that Sathyajith is the right person for her, Mayil falls in love with him, to the point of refusing an opportunity to attend a teacher-training course in Madras to remain with him. Despite loving Sathyajith, she does not allow him to exploit her sexually, which disappoints him. Never intending a serious relationship with Mayil, he proceeds to his native place to get married to another woman. When Mayil begs Sathyajith not to leave her, he says he befriended her for pleasure—not marriage.

A dejected Mayil confesses this to Guruvammal, who quickly plans to betroth her to someone else. The village ruffian Parattai—who lusts for Mayil—spreads rumours about her relationship with Sathyajith. Because of this, Mayil's engagement plans are halted and the village becomes hostile to her. Unable to bear the shame, Guruvammal dies and leaves Chappani to take care of Mayil.

Chappani takes good care of Mayil, cheering her up when she needs it. She warms to Chappani, making him more confident and assertive and grooming him and his manners, to the surprise of many in the village. Mayil tells him to slap anyone who calls him "Chappani" and to respond only to those who address him by his name, Gopalakrishnan. When Sathyajith and Parattai call him "Chappani" despite his request to use his real name, Gopalakrishnan slaps them. Mayil and Gopalakrishnan celebrate his newfound courage. An insulted Parattai later beats Gopalakrishnan badly. Mayil saves him, spitting on Parattai for the brutal attack.

Mayil decides to marry Gopalakrishnan, and sends him to the nearby town for buying wedding supplies. Learning of Gopalakrishnan's absence, Parattai goes to Mayil's house and tries to rape her. Gopalakrishnan returns to Mayil's house and pleads with Parattai to leave her. When Parattai refuses, Gopalakrishnan kills him with a rock and is arrested. He promises Mayil that he will return, and she waits everyday for him.

• Kamal Haasan as Gopalakrishnan (Chappani)
• Sridevi as Mayil
• Rajinikanth as Parattai
• Ganthimathi as Kuruvammal
• Sathyajith as Sathyajith
• Goundamani as Koothu

Development

16 Vayathinile was P. Bharathiraja's directorial debut and his first screenplay. It was originally planned to be a black-and-white film titled Mayil and funded by the National Film Development Corporation of India (NDFC), but according to Bharathiraja, the NFDC withdrew at the last minute without specifying a reason. The film was eventually picked up by S. A. Rajkannu who produced it under his banner Shri Amman Creations. Mayil was eventually re-titled 16 Vayathinile, and its dialogue was written by P. Kalaimani. P. S. Nivas was signed as cinematographer, Somnath-Kamalasekharan as art director and R. Bhaskaran as editor. Chithra Lakshmanan and K. Bhagyaraj worked as assistant directors. The latter provided suggestions for scenes and dialogues.

Casting

Bharathiraja wanted Lakshmanan to sign Kamal Haasan for the role of Chappani, expecting to pay Haasan ?15,000 since the actor had received ?17,000 for Aayirathil Oruthi (1975). When Haasan asked for ?30,000, Lakshmanan suggested that Bharathiraja offer the role to Sivakumar since the production unit could not afford Haasan's request; however, Bharathiraja saw Haasan as the ideal choice and agreed to pay him ?27,000. For his character, the actor grew his curly hair long and wore lungis and khadi high-buttoned shirts. In 2017, Haasan recalled, "Years ago, a man sporting a soiled dhoti and shirt came to my office to narrate a script. Had I turned the offer down on the basis of his dirty clothes, I wouldn’t have been here talking to you. After listening to the script, I realised that he was such a genius and the movie was the cult classic , and he was none other than ace Bharathiraja sir". Bharathiraja also recalled that he showed a "handsome Kamal Haasan in an ugly way" as he wanted to prove that characters need not always be attractive, and to break this stereotype in the film industry.

Rajinikanth was cast as the village ruffian Parattai. Bharathiraja stated in 2013 that although had finalised ?3,000 as the salary for Rajinikanth after the latter initially charged ?5,000, he ultimately paid ?2,500 to him. Some years later, he stated that Rajinikanth's salary was lower than Kamal's due to the former not being an established star then, but added that he was uncertain about the exact salary details. 16 Vayathinile marked Rajinikanth's first appearance in a colour film. Since the actor was not fluent in Tamil at the time, Bhagyaraj read him his lines and Rajinikanth repeated them until he mastered them.

Sridevi was cast as Mayil, after whom the film was initially titled. For the role of Mayil's mother Kuruvammal, Bharathiraja wanted someone who could speak the village dialect fluently and chose Ganthimathi for her acting style. Receiving a salary of ?150, Bhagyaraj was initially considered for the veterinarian's role but wanted to concentrate on directing; despite that, he still made a cameo appearance in the film. The role of the veterinarian went to newcomer Shabbir Ahmed, who was given the screen name Sathyajith during post-production. His scenes were shot in ten days. Sathyajith was not well-versed in Tamil at the time of auditioning. Comedian Goundamani was cast as a character named Koothu. Haasan, Sridevi, Rajinikanth and Gandhimathi were credited by their character names in the opening credits, rather than their actual names.

Filming

Shot mainly in Mysore and Kollegal, 16 Vayathinile was the first Tamil film made completely outdoors and no sets were used. Due to budgetary constraints the technical crew could not afford a camera which could film slow motion and Sridevi had to run in slow motion for the song "Chendoora Poove". The scene where Mayil spits on Parattai required several takes before Rajinikanth insisted that Sridevi actually spit on him for real.

While Bharathiraja wanted the film to follow a linear narration, it was Bhagyaraj's idea to begin the film with a flashback sequence. After the film completed its shoot, it was screened at least 20 times for the distributors and the narrative switched every time between the linear and non-linear versions. Eventually, Rajkannu himself released the film, with the flashback narrative. The budget of the film was ?0.5 million (equivalent to ?10.0 million or US$150,000 in 2017).

16 Vayathinile focuses on rural Tamil Nadu, and the vulnerabilities of Mayil. Film critic Naman Ramachandran compared Parattai to Rajinikanth's character Kondaji from Katha Sangama (1975), stating, "Like in that film, Rajinikanth is a card-playing wastrel with henchmen in tow. Just like the Thimmaraya character in Katha Sangama runs errands for Kondaji, here Chappani/Gopalakrishnan performs services for Parattai, but the similarity ends there because Thimmaraya is evil and Chappani is good." He also described 16 Vayathinile as the first film when a villainous character played by Rajinikanth does not have a change of heart or get away without being punished: "Here he pays for his deeds with his life."

According to Kamal, the film was inspired by David Lean's 1970 drama, Ryan's Daughter. Film scholar Swarnavel Eswaran Pillai noted that the film was marked by "ambiguous and dark protagonists, new subjectivity, avoidance of clichéd and cathartic closures". Kumuthan Maderya, writing for Jump Cut, described 16 Vayathinile as a "neo-nativity" film — a story set in rural Tamil Nadu, valorising the rustic and foregrounding the lives of villagers. Ashis Nandy, in his 1998 book The Secret Politics of Our Desires, noted that doctors in Tamil films like 16 Vayathinile are always viewed with "a bit of suspicion" and remain complete outsiders "capable of seducing women and polluting the community".