In the beginning we apparently see Naina running, but Preity Zinta had fallen and injured herself. Nikhil Advani got a model to jog in front of the camera instead.
Karan Johar had written the script with his friend Kareena Kapoor in mind as the leading lady. But she asked for too high a fee and was replaced by Preity Zinta.
During the title song, "Kal Ho Naa Ho," at the scene where Aman
and Naina are dancing in the night, after Aman touches Naina with the rose, it shows him throw the rose behind him, and at the end of the embrace the rose reappears in his hand.
In the scene where Aman Mathur enters the kitchen to look for
Rohit Patel, who has gone for a date with Camilla, he and Kanta Bhen have a conversation in the kitchen, in front of the glass door. The reflection of the boom mic is visible on the glass door.
Rohit Patel: Ladies and Gentlemen! Welcome to Lalaland... Rohit loves Naina but Naina doesn't love Rohit. She loves Aman. But Aman tells Rohit that he shouldn't let go of Naina so easily. So basically Aman is... insane!
Aman Mathur: Frankie Ramdayal, this girlfriend of mine wants me to leave me for you. She says you are cool, sexy, she says your hairstyle is wow! What do I do Sweetu? If I've not seen 'Dil Chahta Hai', so what if I don't know much about hairstyles?