SHAFAQNA (Shia International News Association) -- The court in Milan also decided they did not need to hear testimony from Moroccan club dancer Karima El Mahroug.
Mr Berlusconi's lawyers requested the trial be halted during elections, where he is standing for prime minister.
Both he and Ms Mahroug have denied ever having sex. Sex with a prostitute who is under 18 is a crime in Italy.
Mr Berlusconi is standing in the election, after stepping down from a third term as prime minister in November 2011, when he was replaced by the technocrat Mario Monti.
Lawyer Niccolo Ghedini said Mr Berlusconi would be too busy campaigning to follow the case or attend court - and also feared the trial could influence the election.
But judges rejected the application.
Prosecutors have accused the defence of trying to prolong, and now delay, the trial to avoid a verdict before the election, at the end of February.
Ms Mahroug, better known by her nickname "Ruby Heartstealer", had arrived at the trial to give testimony for the defence.
She has been called twice before, but has failed to show up, apparently because she was on holiday in Mexico.
'Abuse of power'
Mr Berlusconi, now 76, is accused of paying to have sex with Ms Mahroug in 2010 when she was 17.
The billionaire media mogul has admitted sending Ms Mahroug money - but insists he was just making gifts to a friend in need.
Prosecutors say they had sex on 13 occasions.
He denies having had sex with her, and testified that, in any case, she had told him she was 24.
Ms Mahroug also denies having sex with him - or being a prostitute.
Mr Berlusconi is also accused of abuse of power, for intervening after Ms Mahroug was briefly held by police over theft claims.
He allegedly urged police officers to release her, telling them, falsely, that she was a granddaughter of former Egyptian President Hosni Mubarak.
He admits making the phone call, but denies putting police under pressure - and testified that Ms Mahroug had told him she was related to Mubarak.
Mr Berlusconi faces up to 15 years in jail if found guilty.