Many of Mr Anwar's supporters turned up at court to cheer him on
Malaysian opposition leader Anwar Ibrahim has pleaded not guilty at the start of his long-delayed sodomy trial.
Prosecutors say he sodomised a male aide, and they claim that traces of Mr Anwar's DNA were found in medical tests on the man making the allegations.
Mr Anwar has consistently denied the charges, calling them a conspiracy aimed at breaking his increasingly strong political movement.
Homosexual acts are illegal in Malaysia and he faces up to 20 years in prison.
This is not the first time the charismatic opposition leader - who was once the deputy prime minister until his sudden sacking in 1998 - has faced a sodomy claim.
He served six years after an earlier conviction, which was subsequently overturned on appeal. After his release he led the opposition to election gains in 2008.
Mr Anwar represents a major challenge to Prime Minister Najib Razak, whose coalition has held power for more than 50 years.
'Malicious and frivolous'
ANWAR: CONTROVERSIAL FIGURE
1993 to 1998 - Deputy Prime Minister, under Prime Minister Mahathir bin Mohamad
1999 - Jailed for abuse of power, sparking huge street protests
2000 - Found guilty of sodomy with his wife's driver
2004 - Supreme Court overturns the sodomy conviction, freeing him from jail. He quickly emerges as the de facto opposition leader
March 2008 - ruling coalition narrowly wins general election, but with its worst results in 50 years. The opposition makes unprecedented gains
Aug 2008 - Anwar charged with sodomy for a second time, but despite this is soon voted in as an MP
Feb 2009 - Second trial for sodomy starts
Mr Anwar's much anticipated trial has already been delayed many times, and could easily have been put back yet again.
His lawyers tried a last-ditch effort to ask for advanced access to medical evidence, DNA and CCTV tapes, which they say are key in providing a proper defence.
But a judge decided there was no reason to delay proceedings any further, and Mr Anwar finally faced his 24-year old male accuser, Saiful Bukhari Azlan, in the High Court.
Mr Saiful said Mr Anwar had demanded sex in a Kuala Lumpur apartment.
"I was angry and afraid," Mr Saiful told the court, according to Reuters news agency. "I rejected his offer. I said I didn't want to do it."
The prosecution say that Mr Anwar's semen was found in medical tests on Mr Saiful, and say they plan to bring evidence of this to the trial.
Roger Hardy, BBC Islamic affairs analyst
Anwar Ibrahim's political journey has taken him from charismatic student leader to deputy prime minister and now his country's most prominent opposition politician.
He is a formidable political campaigner because of his popular appeal and because he has succeeded in putting together a coalition that straddles Malaysia's ethnic divisions.
This could be a make-or-break moment in Mr Anwar's tempestuous career. For the current Prime Minister, Najib Razzak, putting him on trial is a politically risky strategy.
But Mr Anwar maintains his innocence, and has called the sodomy allegation "malicious" and "frivolous".
"It is trumped up by political masters using the prosecution for that purpose," Mr Anwar told the High Court.
He believes he is only on trial for political reasons, and in an interview with the BBC before the trial, he referred to the claims against him as a "nasty conspiracy".
"We are committed to democratic ideals and some of us may have to pay the price," he said.
Rights groups have also criticised the trial. Amnesty International accused the government of using "the same old dirty tricks in an attempt to remove the opposition leader from politics".
There were huge protests after Mr Anwar's first conviction for sodomy a decade ago. He was freed on appeal in 2004.