The new building -- the Advanced Center for Emergency Response at 1650 West Harrison -- replaces the one on West Congress.
Overnight the old emergency room closed and the new ER opened for patients around 5:30 a.m.
The new medical center is one of three hospitals in the country with a clover leaf design. Rush officials say the design will help improve patient care.
"We've put together many of our interventional specialties, radiology, neurology, neurosurgery cardiology, we've put them together in one place so when a patient needs an intervention of any kind all the specialists will be co-located together and we think that's a real plus both for the patients but also for the doctors to learn and work with each other," said Dr. David Ansell, Rush Chief Medical Officer.
Patients from the old hospital will not be moved to the new one until Sunday morning. The hospital is expected to be fully operational on Monday morning.