Main Prem Ki Diwani Hoon is a film which spans the time of just one month in the life of a bubbly, "modern girl" named Sanjana (Kareena). She is in every aspect the embodiment of a normal girl who tends to fall victim to mood swings, be forgetful, get lost in her music, and fall in love. Simple right? Not for Sanjana. It just so happens she loves not one, but two boys; two boys who ironically have the same name, Prem.
Now if this weren't confusing enough, both Prems are each other's best friend. Although their personalities are different; Prem (Hrithik) is lovable, yet mischievous, while Prem (Abhishek) thinks being a business tycoon affords one the luxury of being treated like royalty. These two friends confide in each other and share everything, which not only includes their innermost secrets, but the love of one girl, Sanjana.
Herein lies the problem. Sanjana ultimately has to choose between the two Prems. We know on whichever one she decides, he will be the Prem that she will love until the end of time. But which one will it be?