Mullum Malarum (transl. 'The Thorn and the Flower' or 'Even a Thorn Will Bloom'; pronounced [muɭɭum maɭaɾum]) is a 1978 Indian Tamil-language drama film written and directed by Mahendran. Produced by Venu Chettiar and V. Mohan, the film stars Rajinikanth, Sarath Babu, Jayalaxmi and Shoba. It marks Mahendran's directorial debut and is partly based on Uma Chandran's novel of the same name, which was serialised in the Tamil magazine Kalki in 1966. Mullum Malarum tells the story of Kali (Rajinikanth), a winch operator of a cable trolley who dotes on his sister Valli (Shoba) since they were orphaned, and clashes with his boss Kumaran (Sarath Babu).

Mahendran read only part of the novel, and developed the screenplay as he wanted, making a visually-focused film without formulaic Tamil cinema conventions he disliked such as melodrama, overacting, excessive dialogue and duets. Since Mahendran had no previous directing experience, cinematographer Balu Mahendra, who was already an established director, assisted him with the screenplay, dialogue, camera angles, casting and editing. Principal photography lasted for about 30 days, taking place primarily in Sringeri, Karnataka, though some scenes were also filmed in Ooty, Tamil Nadu. The film was edited by D. Vasu, and the soundtrack was composed by Ilaiyaraaja.

Mullum Malarum was released on 15 August 1978. Although it opened to tepid box-office earnings, positive reviews from critics and favourable word of mouth in later weeks helped make it a success with a theatrical run of over 100 days. The film received praise primarily for Rajinikanth's performance, Balu Mahendra's cinematography, Ilaiyaraaja's music, Mahendran's writing and establishing Tamil cinema as a "visual medium". It won the Filmfare Award for Best Film – Tamil, the Tamil Nadu State Film Award for Best Film and Rajinikanth won the Tamil Nadu State Film Award Special Prize for his performance.

Mullum Malarum became a breakthrough for Rajinikanth as an actor and a milestone of Tamil cinema for focusing prominently on visuals and realism without the formulaic Tamil cinema conventions that Mahendran disliked. He continued following this style in all his later films. The film's success inspired a Malayalam remake titled Venalil Oru Mazha in 1979, a Telugu remake titled Seethamma Pelli in 1984, and a Hindi version titled Pyari Behna in 1985.