DeGeneres, a comedian and talk-show host, joined "Idol" in its ninth season, but said she decided a couple of months ago not to return for its upcoming 10th.
"Dim the lights ... I've voted myself off American Idol," she tweeted.
"It was hard for me to judge people and sometimes hurt their feelings," she said.
"I am very grateful for the year I had. I am a huge fan of the show and will continue to be."
Longtime "Idol" judge Simon Cowell left the show at the end of last season, leading to rampant speculation about who might take over for him. Now the show will have to replace two judges.
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