Family members had called the ambulance after the man began to get agitated, saying he wanted to go to Rome to report a drug-trafficking ring, according to a police statement.
But when the emergency services arrived at the apartment building in Empoli, Tuscany, he immediately went to the street and got into the driver's seat of the vehicle.
The incident took place at around 4am on Monday morning.
The 34-year-old drove for around 150 kilometres before being stopped by police on the A1 highway near Siena.
The map below shows an approximation of the journey.
Highway police were able to stop the stolen ambulance after tracking it down through GPS, and organized a road block to alert other vehicles to the possible danger.
The man was already known both to health services and the police, having stolen a bus and driven it into a church wall several years ago, according to local newspaper Il Tirreno.
He has been charged with theft and is in the care of the local health authority.