The vote comes after a recent ANSA poll showed approval for scandal-plagued Berlusconi, his government and his People of Freedom party had fallen to an all-time low.
The March 10 poll showed Berlusconi's personal approval rating fell 2 percentage points to 44 percent, the lowest since he took office two years ago.
About 41 million Italians, two-thirds of the population, are eligible to vote in the two-day election in 13 of 20 regions.
The BBC reported controversies that have dogged Berlusconi could hurt the People of Freedom party's chances at a time when voters are already jittery over high unemployment and a weak economy. The party controls only two of the 12 regions where balloting will take place.
In July, Berlusconi admitted spending a night with an escort, saying, "I'm no saint," but denied paying for sex.
In June, the 71-year-old billionaire denied allegations he paid prostitutes to attend parties at his official residences while photos showed a topless woman and a naked man at his Sardinia villa and a celebrity using the prime minister's official jet, the BBC said.
That came the month after his wife said she was divorcing him because he attended the 18th birthday party of a "female friend."
Last week, Italian media reported Berlusconi was under investigation for allegedly attempting to pressure Italy's communications watchdog to block TV talk shows critical of his government.
The BBC said an investigation into building contracts for earthquake-ravaged L'Aquila had implicated Berlusconi's civil protection chief, Guido Bertolaso.