Pussycat Doll Nicole Scherzinger explained this song to MTV: "All of us started with a dream. I know when I was young, and I would sign people's notebooks, I wrote, 'Remember me when I'm famous,' and I don't know of a little kid who hasn't aspired to be someone. The lyrics go, 'When I grow up, I wanna be famous, I wanna be a star, I wanna be in movies,' but there's a twist at the end, because it says, 'Be careful what you wish for, because you might just get it.'"
Britney Spears, herself a high profile casualty of fame, shot a cameo for the song's video, but it was dropped from the final edit. It would have been the second time that the "Toxic" hitmaker had performed with the Dolls as Spears had previously joined them on stage during a private performance at her older brother Bryan's birthday party in 2004.
Rodney Jerkins wrote this with the songwriting brothers Theron and Timothy Thomas, who go by the name of Rock City. The song samples the main riff of The Yardbirds 1966 track "He's Always There," which was originally on their Roger the Engineer album. Because of the sample, that song's writers - Jim McCarty and Paul Samwell-Smith - also receive writing credits on "When I Grow Up."