The ambulance apparently collided with a car, which then struck a pole in the 2600-block of West 95th Street in south suburban Evergreen Park.
The ambulance flipped onto its side with two emergency medical technicians inside.
Police believe the ambulance caused the accident by rear-ending a car in the center lane, which started a chain reaction crash that ended with the ambulance going over the curb and tipping over.
There was no patient in the vehicle at the time, but the emergency medical technicians were slightly injured.
A woman in the car was taken to the hospital as a precaution.
The driver of the ambulance was cited.