Campaigners for a new West Herts hospital have branded Watford general's one-star hygiene rating as "not acceptable" and "particularly disturbing".
An environmental health officer raised serious concerns after visiting the ward kitchen at the hospital on in November last year.
The officer gave a hygiene rating of just one-star out of five - the second-lowest rating - concluding that major improvement is necessary.
The New Hospital Campaign - who are calling for a new A&E facility to be built on greenbelt land in West Hertfordshire - have slammed the report's findings.
Spokesperson Edie Glatter said: "Considering that the hospital is feeding very vulnerable people it is particularly disturbing and could be putting patients at risk.
"We should expect hospitals, care homes and schools to get a rating of 5. This is not acceptable. Many eating places routinely achieve a five rating."
The Food Standards Agency website says major improvement is needed in food safety management, including whether checks are in place to ensure food is safe to eat.
Improvement is also required in hygienic handling of food preparation, cooking, reheating, cooling, and storage.
Watford General Hospital said immediate changes have been made after the hygiene report, which was published on the Food Standards Agency website.
West Herts Hospitals Trust director of environment Paddy Hennessy said: “We are very disappointed with this rating which does not meet the high standards of care we hold for our patients.
"Since the inspection we have replaced equipment and implemented checks and audits to ensure the food handling environment is safe for our patients.
"We are also providing enhanced training for all staff who handle food so there are strong food safety management procedures in place.
"I would like to reassure the public that our patient food is safe and we look forward to the next inspection where we can demonstrate the improvements and the progress we have made.”