Congresswoman Gabrielle Giffords, who was shot in the head in Tucson, Arizona, a year ago, is to step down this week from the US Congress to focus on her recovery.
She was shot through the head on 8 January last year when a gunman killed six people and wounded 12 others.
In a posting on several social media sites on Sunday, Ms Giffords says she is getting better, but it is best that she stand aside.
"I have more work to do on my recovery, so to do what is best for Arizona I will step down this week," she said on Twitter and YouTube.
"I'm getting better. Every day my spirit is high. I will return and we will work together for Arizona and this great country. Thank you very much," she added.
Ms Giffords was serving her third term. She now walks and talks with difficulty.
Her office said she would submit her letter of resignation this week to House Speaker John Boehner and Arizona Governor Jan Brewer.
Governor Brewer said Arizona law required her to hold a special election to determine a replacement.
Gunman Jared Loughner, 23, a college dropout, has been declared unfit to stand trial.