Adams, the 24-year-old from Bakersfield, Calif., with the pink hair, "always made us laugh," host Ryan Seacrest said after a video tribute to Adams, who accepted her exit gracefully.
"I just want to say thanks to everybody who got me here - friends, fans, everybody," Adams said after learning her fate.
More than 20 million viewers voted after Tuesday's live "American Idol" episode, in which the finalists sang for judges Simon Cowell (search), Paula Abdul (search) and Randy Jackson (search) - who were joined by celebrity judges Ashford & Simpson.
After the performances, Cowell said he thought Adams looked like "Jay Leno's sister," alluding to the lantern-jawed host of NBC's "Tonight Show."
The winner of "American Idol," which is averaging north of 18 million viewers an episode, snares an RCA recording contract and heavy promotion for his or her first single.
Kelly Clarkson won the first "AI" show, and was followed last year by "The Velvet Teddy Bear," Ruben Studdard, who won the second edition of the show.