Though the film's shooting happened over 2 months, Kamal Haasan allegedly filmed his scenes in 5 days straight.
In the Hindi version, The Wednesday, Naseeruddin Shah had an edge over Anupam KherAfter with regard the dialogues, But, when Mohanlal was cast, extra scenes and dialogues were written for him.
Though Kamal Haasan wrote the film's dialogues aliong with ER Murugan, the director of the original, Neeraj Pandey, was credited for dialogues in the film.
Despite being a remake of The Wednesday, .UPO had an entirely different sound track, composed by Shruti Haasan, in her music debut. The theme song'Vaanam Ellai...Illai' wasn't featured in the film.
UPO was the First tamil film to be shot in Red One Digital camera
The film's title, which was originally Thalaivan Irukkiran, was changed to Unnaipol Oruvan in early April 2009, a couple of months before the release.
Bharath Reddy, Shriya Reddy's brother and Vishal's brother-in-law, played one of the cops in the film, while the other cop role was essayed by Ganesh Venkataraman,
In one of the calls made to the commissioner's mobile, Kamal uses his own mobile phone rather than using the array of temporary, stripped down phones with fake sims. This was a goof-up by the team.
For the UK release, the distributor chose to remove one shot in order to obtain a 12A classification. The shot removed depicted a police suspect involuntarily urinating while under interrogation.
Anuja Iyer's smoking habit was an on-the-spot idea by Kamal Haasan, which he thought defined Natasha's free -spirited character well.
Unnai Pol Oruvan gers referenced at the movie theatre in Suriya's 2010 film, SIngam. There are posters of UPO all around in the scene,
