Senator Kennedy was treated at the Massachusetts General Hospital
US Democratic Senator Edward Kennedy has left hospital after being diagnosed with a malignant brain tumour.
Mr Kennedy was released ahead of schedule on Wednesday after having recovered from treatment "remarkably quickly", doctors said.
Mr Kennedy, 76, was flown to a hospital in Boston from his home in Cape Cod after suffering a seizure on Saturday.
The youngest brother of assassinated President John F Kennedy, he is one of the best-known Democratic politicians.
Doctors at Massachusetts General Hospital said Mr Kennedy had recovered quickly from a biopsy performed on Monday.
"He will return to his home on Cape Cod while we await further test results and determine treatment plans," doctors Lee Schwamm and Larry Ronan said in a statement.
"He's feeling well and eager to get started."
On Tuesday, the doctors said tests had revealed a tumour in the left side of Mr Kennedy's brain.
"Preliminary results from a biopsy of the brain identified the cause of the seizure as a malignant glioma in the left parietal lobe," they said.
Mr Kennedy is the second longest-serving member of the Senate. He has been an active supporter of Barack Obama for the Democratic nomination for US president.
Mr Kennedy was first elected senator for Massachusetts in November 1962 - shortly after turning the requisite 30 years of age - to replace his brother, who had been elected president in 1960.
EDWARD MOORE KENNEDY
1932 Born, youngest of nine siblings
1962 Becomes country's youngest senator
1963, 1968 Brothers President John F Kennedy and Senator Robert F Kennedy both assassinated
1969 "Chappaquiddick incident" - Kennedy flees scene after road crash in which his young female passenger dies
1980 Runs unsuccessfully for Democratic nomination against sitting President Jimmy Carter
Since then he has been re-elected seven times.
Born into a rich and powerful Irish-American Catholic family, the son of Joseph Kennedy, Edward "Teddy" Kennedy became the head of the clan after the death of his three elder brothers.
The eldest, Joseph Jr, was killed while flying a bomber during World War II.
John was assassinated while president in 1963, and Robert was shot dead while running for president in 1968.
Edward, or Teddy, as he is known, ran against sitting President Jimmy Carter in 1980, but failed, after struggling to put the infamous "Chappaquiddick incident" behind him.
He had, in 1969, crashed a car off a bridge, and while he escaped, his young female passenger drowned in the water below. He fled and did not report the incident to police for more than eight hours.
He later pleaded guilty to leaving the scene of an accident and received a suspended two-month sentence.
Mr Kennedy is also the father of Congressman Patrick J Kennedy.