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.

Munna Bhai - Sanjay Dutt: Laughter, they say, is the best medicine. Love, Munnabhai says, works even better. He hugs people, giving them 'jadu ki jhappi'. Naturally then, though he can barely tell a liver from a lung, he is the best doctor in town.

Hari Prasad Sharma - Sunil Dutt: Upright, principled and unfailingly righteous, Hari Prasad Sharma is a throwback to a bygone era. His conscience, like the pagdi on his head, is spotless. Imagine then, the heartbreak, when he discovers that his own son who he believes to be a doctor is a tapori called Munnabhai.

Suman - Gracy Singh: Dr. Suman's calm demeanour goes for a 'full toss' after she encounters Munnabhai. He makes her laugh and cry and teaches her that sometimes a loving hug or the 'jadu ki japhi' works better than all the medicines in the world.

Zaheer - Jimmy Shergill: Zaheer is a young man struggling to fulfil his responsibilities and make his dreams come true. But his fight for a future is abruptly hobbled by cancer. Now all that he seeks is Munnabhai.

Dr Asthana - Boman Irani: Dr Asthana is Hitler with a heart. A strict disciplinarian, he lives life by the rules. But he is also a believer in laughter therapy and in his most stressful moments breaks out into manic laughter. Munnabhai naturally is the deeply imbedded thorn in his side.

Circuit - Arshad Warsi: Circuit is Munnabhai's one man army. What ever Munna needs - from a dead body to advice on love and marriage - Circuit can provide it. He is a tapori Lakshman for a tapori Ram.