Munnabhai (Sanjay Dutt) is a happy man. He lives with his gang in the bylanes of a 'dhobi ghat' in Mumbai; takes pride in being a 'social worker' (they actually settle 'financial disputes' through 'dadagiri'); and enjoys his booze, babes, brawls followed by a good night's sleep. Not much bothers Munna. Except his parents' annual visit from the village. Munna's father, Hari Prasad Sharma (Sunil Dutt), an upright, moralistic man believes that his son is actually a doctor running a charity hospital. Every year, when his parents arrive, Munna and his gang bathe, shave, don white coats and stethoscopes and pretend to be diligent doctors.

This year, however, the clever charade falls apart. Hari Prasad Sharma runs into an old friend, Dr. Asthana (Boman Irani), who has a daughter called Suman (Gracy Singh). The two decide that their children, both doctors, would make a perfect match. Munna tries hard to save the situation, but his father discovers the truth. And all hell breaks loose. Hari Prasad Sharma, now broken by the truth, removes his white spotless 'pagadi' and cries. Munnabhai then takes a decision that would change many lives : He decides to become a doctor. Munnabhai MBBS is a hilarious and heart warming story of a local goon's journey into the medical world - a place he neither belongs to nor believes in. It is a classic story of a right man in a wrong place.