Derriford Hospital in Plymouth has "not made enough progress" in the past few months and has been warned it must make further improvements.
Inspectors from the Care Quality Commission say some progress has been made since the summer 2019 inspections, but identified four key areas which are not up to standard.
Overall the health trust is rated as "requires improvement", with particular focus on emergency services, medical care, surgery and diagnostic imaging.
Meanwhile critical care, maternity, children's services and outpatients have made progress and are now rated as good.
The inspectorate said there was "always more that can be done" but that it was "disappointing" more had not.
Alternatives to A&E:
Patients are instead advised to consider visiting a minor injury unit, a pharmacist or their local GP.
The NHS 111 number is also available for people who urgently need medical help or advice but are not in a life-threatening situation.