When the producers tried to buy the rights of Frank Zappa's "Watermelon in Easter Hay" they were told by Zappa's family that Zappa requested that three of his songs were never played in any media except the album where they appear and that song was one of them. Gail Zappa, Frank's widow, saw the movie when editing was almost completed and agreed to make an exception because she considered that Zappa would be proud of the movie.
Broke Mexican Box office records on June 8th, 2001, grossing $2.2 million in its first week, the biggest opening ever for a Mexican film.
Alfonso Cuarón did not want to cast Luna for the role of Tenoch because he was a teen idol and soap opera star. Bernal convinced Cuarón to hire Luna because their strong existing friendship would make the performance of their characters' friendship much easier. Cuarón ultimately hired Luna because he became convinced that their bond would produce a natural and honest performance.
Cinematographer Emmanuel Lubezki said he used "90% natural light". Only some scenes have additional lighting. [2015]
The ending scene where they talk while having a coffee was the first scene filmed.