The ruling, like most things involving Mr. Berlusconi, polarized Italy. It shook the governing coalition, in which Mr. Berlusconi’s center-right party is participating, but was not expected to topple it. The former prime minister, who denies wrongdoing, does not immediately have to leave his seat in Parliament while the case faces two rounds of appeals.

The trial, involving a young woman named Karima el-Mahroug, nicknamed “Ruby Heart-Stealer,” had become the most personal, and tawdry, of Mr. Berlusconi’s many legal sagas. The courtroom testimony of after-dinner entertainment at Mr. Berlusconi’s villa near Milan — accounts that varied from PG to X-rated depending on the witnesses — enthralled some Italians but irritated others, who wondered how it was possible that he could remain in politics in light of his legal woes.

Demonstrators, both pro- and anti-Berlusconi, gathered outside the Milan courthouse on Monday.

Mr. Berlusconi, 76, who is widely seen as remaining in politics to keep his parliamentary immunity and to protect his business interests, has vehemently denied the charges, accusing prosecutors of being on a left-wing witch hunt against him. His lawyers had tried to change the location of the trial, arguing that the Milanese judicial milieu was biased against Mr. Berlusconi, who has faced several trials in that city.