"You had the audacity to go on national television, show the world what you did and dare the legal system to stop you. Well sir, consider yourself stopped," said Judge Jessica Cooper.

"This trial was not about the political correctness of euthanasia. This was about you, sir," the judge added.

Family pleads for clemency

Rob Watson in Washington: The judge was tough

The defence had asked for a suspended sentence, citing the victim's family statements during the sentencing hearing and the Dr Kevorkian's age. He will be 71 in May.

The retired pathologist says he has helped more than 130 people die since 1990.

The wife and younger brother of Thomas Youk, the man Dr Kevorkian was convicted of killing, called on the judge to show compassion and grant the assisted suicide advocate clemency.

Thomas Youk: Death shown on US TV

"It troubles me that the jury has heard only one distorted version of this story, and I wonder aloud, 'can this be justice?'" said Thomas Youk's younger brother Terrence.

Prosecutors asked for a minimum of a 10-year sentence. He has previously been acquitted by three juries on assisted suicide charges. A mistrial was declared in a fourth trial.

"This case is about what Jack Kevorkian did, and what he did under the law under the state of Michigan is commit murder," the prosecutor said.

Death on TV

The judge and the prosecutor made a point that Kevorkian provided a videotape of Mr Youk's death to the television programme "60 Minutes," and challenged the legal system to stop him.

Mr Youk suffered from a wasting disease. Before he died, he was confined to a wheelchair, and had difficulty breathing and eating.

During Mrs Youk's statement, she said, "the tape was produced for no other reason then to show my husband's consent."

Dr Kevorkian has previously threatened to go on hunger strike if convicted and jailed.