A spokesman at the Hadassah hospital in Ein Kerem said Mr Sharon, 77, had lost consciousness but regained it shortly after.
"I feel fine," Mr Sharon was quoted as saying by aides.
Israeli television said he had quipped to doctors: "You're not getting rid
of me yet."
Mr Sharon felt unwell after meeting veteran statesman Shimon Peres at his Jerusalem office and was rushed to nearby Hadassah hospital for a brain scan.
Tests revealed a minor stroke. Doctors said Mr Sharon was likely to stay in hospital for several days days.
"There is no reason for fear," said his personal physician Boleslav Goldman.
"The prime minister arrived at the hospital at 8:05 pm (1805 GMT)," Yuval Weiss, deputy director of the hospital, said in a brief statement to reporters.
"He is fully conscious and he will be undergoing further exams."
Undergoing treatment
The spokesman said that Mr Sharon had not needed any "invasive procedure" but gave no further details about his treatment.
The cabinet secretary Israel Maimon and Sharon's two sons Omri and Gilad arrived at the hospital around an hour after the prime minister was admitted shortly after 8:00 pm (1800 GMT), an AFP correspondent at the scene reported.
Mr Maimon said that Mr Sharon's condition would not necessitate the appointment of an interim premier.
"As the prime minister is functioning normally, is speaking and is communicating with members of his family, there is no need to name an interim prime minister," he told reporters outside the hospital.
Mr Maimon said that Mr Sharon had asked to leave hospital but doctors had recommended he stay in for observation.
If Mr Sharon were to be incapacitated, Finance Minister Ehud Olmert, who is also deputy premier, was expected to stand in.
Mr Sharon, who turns 78 in February, underwent surgery last year and also had a cancerous growth removed from his face in a Tel Aviv hospital the year before.
Finance Minister Ehud Olmert, who is also deputy prime minister, will take over from Mr Sharon in the event that the premier is incapacitated.
Mr Sharon is running for re-election on March 28 as the head of a new party called Kadima which he established on November 21 after quitting the right-wing Likud party.
The former general, who was first elected prime minister in 2001, would be 82 if he were to win re-election and then complete a full term in office.
Leaders react
Palestinian leader Mahmud Abbas has
telephoned Mr Sharon's office to wish him a speedy recovery following the stroke, a Palestinian statement said.
The White House said that it hoped Mr Sharon would make a quick recovery.
"We've seen the reports (on his health) and we wish the prime minister a full and speedy recovery," White House spokesman David Almacy said.
Mr Sharon, who suffers from a weight problem, has cut down considerably on his overseas travel in recent years but still sustains a punishing work schedule.
Quite apart from splitting from the Likud party which he helped found in the early 1970s, Mr Sharon has also overseen the pullout of Israeli troops and settlers from the occupied Gaza Strip in the last 12 months.
He hosted a meeting of the Israeli cabinet on Sunday morning and was reported to have met with the former Prime Minister Shimon Peres.
Born in British-mandate Palestine in 1928, the prime minister began his military career at the age of 17 and first came to prominence on the battlefield in Israel's wars against Arab states such as Egypt.
As defence minister, he masterminded the 1982 invasion of Lebanon and siege of Yasser Arafat's Palestine Liberation Organisation headquarters in Beirut.
The following year, he was forced out in disgrace after being held "indirectly responsible" for the massacres at the Palestinian refugee camps of Sabra and Shatila in Lebanon perpetrated by his Christian Phalangist allies.
Despite the commission's recommendation that Sharon was unfit for public office, he slowly rebuilt his reputation before becoming leader in 2000 of Likud, the party he helped develop, and rising to the pinnacle of government.
Mr Sharon's wife Lily died of cancer five years ago while his first spouse, Lily's younger sister Margalith, died in a car crash in 1962.
Sons Omri and Gilad have worked closely with their father during his political career. A third son, Gur, died in October 1967 after being shot while playing with his father's rifle.