Silvio Berlusconi has always denied any wrongdoing
Italy's former PM Silvio Berlusconi has been sentenced to seven years in jail and banned from public office for having sex with an underage prostitute.
The Milan court ruling is not effective until several appeals have been heard.
Both the 76-year-old media tycoon and the Moroccan woman concerned, Karima El Mahroug, had denied the claims.
Mr Berlusconi is already embroiled in several other court cases. In October 2012 he was given a four-year sentence for tax fraud, also under appeal.
In the latest court ruling he was convicted of paying for sex with Ms El Mahroug, known as "Ruby the Heart Stealer", in 2010, even though she was just 17 at the time.
Although frequenting prostitutes is not a crime in Italy, having sex with one who is under the age of 18 is an offence punishable by a prison sentence.
He was also found guilty of abusing his prime ministerial powers, by arranging to have her released from police custody when she was detained in a separate petty theft case.
Ms El Mahroug was one of a group of women invited to Mr Berlusconi's private residence for so-called "bunga-bunga" party evenings.
The prosecution said these women were part of a prostitution system set up for his personal sexual satisfaction.
The judges sentenced Mr Berlusconi to seven years in jail - one year more than the six-year term demanded by the prosecution.
As soon as he heard the verdict, Mr Berlusconi's lawyer Niccolo Ghedini announced an appeal.
"This is beyond reality," Mr Ghedini told reporters outside the court. "The judges even went beyond the prosecutors' request."
The judgement could have major political repercussions for Italy, analysts say.
They say a guilty ruling could weaken current Prime Minister Enrico Letta's coalition government, which depends on the support of Mr Berlusconi's centre-right party, People of Freedom (PdL).
But Mr Berlusconi will not have to spend any time in jail unless a lengthy appeals process is exhausted.
Even then, he may escape prison because of lenient sentencing rules for people over the age of 70.