This was the first time superstar Amitabh Bachchan sang a playback song for a movie. "Mere Paas Aao" was the first of many songs of a movie sung by him.
The film was originally titled after the famous con artist Natwarlal, but as he was offended by this his lawyer sent a legal notice to the producers and later the film was re-titled Mr. Natwarlal only days before its release.
Tito&Tony signed Amitabh/Rekha for "Natwarlal". When the shooting completed, they were told that the title is registered with another maker. T&T then opted for to add "Mr" to the title. But that maker lodged complaint with FPA that "Natwarlal" and "Mr Natwarlal" are same (as Natwarlal can be only a Mr).And he won again!! Traumatised T&T finally came up with the one -"Amitabh Bachchan In And As Mr Natwarlal",which didn't have any further objection.The censor certificate also bears the same.
During the shooting of the film the tigeress Bharati fell in love with Amitabh. During lunch break she refused to eat her food. Her handler Mr. Govindraj was wondering if she was sick and would need a doctor. Then as soon as Amitabh came on to the set and met the tiger and began eating, the tiger returned to her food. From then on the tiger only would eat after Amitabh did.
Kasam Paida Karnewale Ki and Adventures of Tarzan (1985) used the background music/ title of the film Mr.Natwarlal.