Berlusconi, who was holding a ministerial meeting in Rome, did not attend the hearing, which lasted seven minutes and was devoted to formalities. The trial was adjourned to May 31.
Dozens of police patrolled the courthouse in downtown Milan. More than 100 journalists attended the opening session, while satellite TV trucks lined the streets surrounding the monumental Fascist-era courthouse.
Unlike Berlusconi's other trials, the one that opened Wednesday puts the premier's personal life under scrutiny, and a conviction could end his political career. He denies wrongdoing.
Prosecutors allege Berlusconi paid Moroccan teenager Karima el-Mahroug, known as Ruby, for sex at his villa in Arcore, then called police to have her released from custody when she was picked up for theft out of concern that she would reveal their relationship. She was 17 years old at the time.
Both the 74-year-old premier and el-Mahroug, who has turned 18 in the meantime, have denied having sex.
El-Mahroug's lawyer, Paola Boccardi, said her client would not seek to become a civil complainant in the trial, a move that would have allowed her to seek financial damages in the case of a guilty verdict and would have given her legal team the ability to question witnesses.
Boccardi said that declaring el-Mahroug a civil complainant would have been an admission of the accusations that she had been paid to have sex with Berlusconi - something she strongly denies.
"This contrasts with what Karima has always declared. She has always said she was never the object of sexual acts by Premier Berlusconi, and she has never made the choice to be a prostitute," Boccardi said. "Karima does not believe herself to have suffered any damage for having been present at Arcore, or having visited with the premier" in the Milan suburb.
Police officials who were contacted by the premier or his office the night that el-Mahroug was taken into custody also have decided not to declare themselves civil complainants.
Berlusconi's defense and political allies are trying to get the trial moved out of the Milan tribunal, which the premier maintains is politically slanted against him. They want the case transferred to the Tribunal of Ministers, which deals with offenses committed by public officials in the execution of their duties.
Parliament on Tuesday asked the country's Constitutional Court to decide whether the authority should be the Tribunal of Ministers. The Tribunal of Ministers would need parliament's authorization to proceed with the trial - something that would likely be denied in a Berlusconi-controlled house.
Berlusconi's lawyer, Giorgio Perroni, said the defense team would decide in the coming weeks if they will seek to have the trial suspended until the Constitutional Court can rule on the jurisdiction.
The premier's defense argues he called police officials seeking el-Mahroug's release from custody because he believed at the time that she was the niece of then-Egyptian President Hosni Mubarak, and he wanted to avoid a diplomatic incident.
The underage prostitution charge carries a possible prison term of six months to three years. The abuse of office charge is even more dangerous: it carries a sentence of four to 12 years, and if Berlusconi is sentenced to more than five years, he would be barred from ever again holding public office.
George Clooney, Italian Cabinet ministers and aspiring starlets have been called to make appearances at the trial, though the court must decide which witnesses to admit.
Outside, Berlusconi supporters swapped insults with opponents of the premier but the heavy presence of riot police prevented any real scuffles.
Berlusconi supporters have maintained a vigil on a traffic island opposite the courthouse since court procedures against the premier resumed in February, after a high court weakened the premier's immunity. Three other active cases involve corruption and tax fraud allegations.
"We want to give the premier strength to resist the injustices," said Maria Grazia Piracci, an out-of-work advertising saleswoman.
Berlusconi opponents, meanwhile, held their own gathering across the street. Some voiced their support for the court system, with signs reading "Magistrates, don't give up," while others expressed anger at Berlusconi's leadership.
"I am fed up with those who support him without dignity. I don't feel represented by this person. I'm embarrassed to have a president like him," said Maria Antignani, a retiree.
