A hospital was forced to close its A&E department due to computer network issues.
Cambridge University Hospitals (CUH) trust declared a "major incident" at Addenbrooke's on Monday afternoon.
Patients were urged to choose alternatives while the A&E was closed and the advice continued after the issue was resolved.
A CUH statement said: "Cambridge University Hospitals can confirm computer network issues have now been resolved.
"However, patients are advised that our Accident and Emergency department is still extremely busy and as a consequence we remain in major incident.
"CUH would like to thank patients and staff for their support during this incident."