An Illinois congressman being treated for bipolar disorder and facing scrutiny from ethics probes has resigned weeks after his re-election.
Jesse Jackson Jr, son of civil rights activist Rev Jesse Jackson, was largely absent from Congress in recent months.
In his resignation letter, Mr Jackson, 46, told Speaker John Boehner his constituents "deserve a full-time legislator".
He was re-elected in a heavily Democratic district on 6 November 2012.
He was first elected to the House of Representatives for the Illinois second congressional district, which includes part of Chicago's South Side and some suburban areas, in 1995.
'Share of shortcomings'
Mr Jackson first disappeared from Congress in June, with it later being revealed that he was undergoing treatment at the Mayo Clinic in Minnesota for bipolar disorder and gastrointestinal issues.
He returned to his Washington home in September but went back to the clinic the next month. Rev Jackson said his son had not yet "regained his balance".
Announcing his resignation on Wednesday, Mr Jackson suggested he still faced a struggle to resume full health and fitness.
"The constituents of the district deserve a full-time legislator in Washington, something I cannot be for the foreseeable future," he said.
"My health issues and treatment regimen have become incompatible with the House of Representatives."
Mr Jackson has also been under investigation by the House Ethics committee over his dealings with jailed ex-Illinois Governor Rod Blagojevich. There have also been reports of a new federal probe into possible misuse of campaign money.
In his letter, he acknowledged the House probe for the first time, saying he was "doing my best to address the situation responsibly, co-operate with the investigators, and accept responsibility for my mistakes".
"None of us is immune from our share of shortcomings or human frailties and I pray I will be remembered for what I did right," he added.
His seat in Congress will now be filled by a special election, the same way Mr Jackson was first elected.
His resignation is not expected to result in any changes in the political balance of power of the House of Representatives, which is controlled by Republicans.