When Naina's family prays, there's a continuity error. Naina's younger brother's position changes.
During the fight between Sushma Seth and Farida Jalal when Preity enters she has snow in her hair and in the long shot it's missing.
During the title song "Kal Ho Naa Ho," the scene where Aman
and Naina are dancing in the night, after Aman touches Naina with the rose, he throws it behind him, and at the end of the embrace the rose reappears in his hand.
In the start of the song "It's the Time to Disco" the sound of a zipper being opened is heard much before Preity Zinta actually opens the zipper of the jacket.
When Naina returns home from Central Park, her lips say, "St Paul's Cathedral."
When Rohit asks Naina to join Salsa classes along with him, Naina's reply isn't properly lip synced. She says "Nahi" but it's heared "Nahi Rohit".
When Aman Mathur enters the kitchen to look for Rohit Patel, who has gone on 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.
Throughout the film, shots of New York are interposed with similar shots of Toronto. The film tries to make the viewer believe that the Toronto shots are, in fact, New York, but the architectural styles and obvious Toronto landmarks are completely different than those found in New York.
At the end of the "Pretty Woman" musical sequence, Jaswinder misses the cue to begin clapping.
Preity takes off her glasses she can't see anything but then later in the film she can see without specs.