The trust said patients' safety "is the highest priority" at the hospital
A Herefordshire hospital which received the lowest score in a report by a monitoring body says it is "responding proactively" to the findings.
Hereford Hospitals NHS Trust is "significantly underperforming", the report by Dr Foster said.
Eleven other NHS hospital trusts in England also received the lowest score.
In a statement, chief executive Martin Woodford said the safety of patients was "the highest priority" at Hereford County Hospital.
He said: "As a trust Hereford Hospitals is responding proactively to the findings of the Dr Foster report."
The part-private, part-NHS Dr Foster Hospital Guide rates hospital trusts from one to five based on analysis of a range of "safety indicators", including errors in surgery, deaths, infection rates and staffing levels.
The report by Dr Foster also said 27 trusts had unusually high death rates.
Overall, the report said hospital death rates in England had fallen by 7%, but quality of care continued to vary greatly across the country.
It cited more than 200 cases where items such as swabs had been left inside patients' bodies after surgery and more than 5,000 instances where people who were admitted with low-risk conditions died in hospital.