Sattam Oru Iruttarai (transl. The Law is a Dark Room) is a 1981 Indian Tamil-language vigilante action film written and directed by S. A. Chandrasekhar, from a story by his wife Shoba. The film stars Vijayakanth, Poornima Devi and Vasumathi, with Sangili Murugan, Nithin and Chowdry in supporting roles. It revolves around a man who seeks to kill three men to avenge his father and elder sister, while his other sister, a police inspector, wants to thwart them the legal way.

Sattam Oru Iruttarai is the second film directed by Chandrasekhar. It was released on 14 February 1981, and became a major commercial success, inspiring more Tamil films with themes about the law system which were mostly directed by Chandrasekhar. The film was remade in Telugu as Chattaniki Kallu Levu (1981), in Malayalam as Maattuvin Chattangale (1982), in Kannada as Nyaya Ellide (1982), in Hindi as Andhaa Kaanoon (1983) and again in Tamil under the same title (2012).