Video showed the prime minister with his face bandaged and waving to reporters as he got into a limousine.
Earlier, an aide had said Mr. Berlusconi spent a quiet night at the San Raffaele hospital and was looking forward to returning to work.
Sunday's attack left Mr. Berlusconi with a broken nose and some chipped teeth. Doctors had planned to release the 73-year-old leader from the hospital Wednesday, but kept him under observation for an extra day after he experienced additional pain and had trouble eating.
They have ordered Mr. Berlusconi to restrict his public activities for at least two weeks.
Police say the 42-year-old suspect, Massimo Tartaglia, in the attack has a history of mental illness.
On Wednesday, police overpowered and detained an unarmed man near the hospital room where the prime minister was recovering. They say the 26-year-old man has mental health problems and said he just wanted to speak with Mr. Berlusconi.
Meanwhile, the incident has prompted Italian Interior Minister Robert Maroni to propose giving judges more power to crack down on websites.
Although the attack has triggered an outpouring of support and sympathy for Mr. Berlusconi, some Italians have been praising the attack on social media sites like Facebook.
Before the attack, some Italians had been calling for Mr. Berlusconi to resign because of sex scandals and corruption trials.
Some information for this report was provided by AFP, AP and Reuters.