Thenali Soman (Kamal Hassan) is a Sri Lankan Tamil who has come to Chennai for psychiatric treatment because of numerous phobias caused by his trauma of the Sri Lankan Civil War. Dr. Panchabhootham (Delhi Ganesh) and his assistant (Ramesh Khanna), who are the doctors treating Thenali, are jealous of a relatively junior doctor Kailash (Jayaram) getting all the media attention. They send Thenali over to him, believing that his failure to cure Thenali of his phobias will derail his success. Soon after their first appointment, Kailash heads to his home in Kodaikanal on a vacation with his wife Jalaja (Devayani) and his two children Arjun (Master Suraj) and Aishwarya (Baby Taj Nisha). Kailash tells Thenali to wait until after the vacation before his therapy can begin, but Panchabhootham asks for Thenali to go meet Kailash while on vacation.

The expected happens. Thenali falls in love with Janaki (Jyothika), Kailash's younger sister, which is vehemently opposed by the latter. The whole film is about how Kailash goes mad with Thenali's antics and even begins to suspect that his wife has an affair with Thenali, as she has a soft corner for the latter. He even tries to kill Thenali by tying him to a tree with a time bomb. Thenali, thinking it is a fake bomb used only to relieve him from his fears, removes it and puts it in Kailash's house, causing it to explode. Seeing this, Kailash suffers a paralytic attack. Thenali later marries Janaki.

While Thenali, Kailash, and family are at a picnic, Thenali's long-lost wife shows up and re-unites with him. Enraged, Kailash jumps out of his wheelchair and berates Thenali for ruining Janaki's life, but soon realises this was all a set-up by Thenali to cure Kailash's paralysis through shock treatment, which succeeded; the woman was actually actress Meena, who Thenali hired to pose as his wife.

Kamal Haasan approached K. S. Ravikumar to make the film after the success of the director's Padayappa featuring Rajinikanth and the film took four months to be scripted by K. S. Ravikumar, Kamal Haasan and Crazy Mohan. The story of the film was inspired by the 1991 American film What About Bob? directed by Frank Oz. Mohanlal was the initial choice to play Kailash and actress Simran was the original choice for the role of Janaki, but Jayaram and Jyothika later took the roles. Actress Meena was signed on by the producers to appear in a guest role as herself. Vivek rejected the film as he felt that he "didn't have the best laugh lines". The film was launched at the Kalaivanar Arangam in Chennai on 22 March 2000 with Y. Gee. Mahendra as compere and with Rajinikanth as chief guest.

Kamal Haasan played a Sri Lankan Tamil in the film and to get the accent right, he took lessons from prominent television host, Abdul Hameed. Scenes were shot predominantly in Ooty, while some song sequences were shot in New Zealand.^[13]

The Hindu gave a verdict that the film was "a wholesome mix of rip-roaring action, witty dialogues and exotic locales".^[14] Rediff stated, "the comedy is on a single track in Thenali" and that "it is more tiresome than humorous".^[15]

Thenali completed 175-day runs across halls in South India.^[16] A success meet was also held with Rajinikanth again attending the function, where Ravikumar revealed that it was the actor who picked the title, Thenali.^[17] It went on to win three Tamil Nadu State Film Awards with Thamarai picking up the Tamil Nadu State Film Award for Best Lyricist and S. Maniraj won the Tamil Nadu State Film Award for Best Art Director in the technical award categories. Jayaram received a Tamil Nadu State Film Award Special Prize for his role in the film.^[18]

The film was dubbed into the Telugu language as Tenali under the production of singer, S. P. Balasubrahmanyam and won good reviews.^[19][20]

The soundtrack of the film was composed by A.R.Rahman, with lyrics written predominantly by newcomers. The album also featured the song "Injerungo", which became the first noted song of lyricist Thamarai, who used Jaffna slang within the song.^[21] Due to the rift between Rahman and Vairamuthu the lyricist has been replaced by newcomers.^[22] The song "Swasame Swasame" was re-used in the final scene of the American film The Accidental Husband.^[23]

Tamil

Telugu