An investigation has been launched after a wire was left inside a patient.
The guide wire was discovered on a chest X-ray 12 hours after the patient underwent surgery at Royal Stoke University Hospital.
The so-called "never event" - a medical mistake so serious it should never happen - took place at the hospital in August.
The University Hospitals of North Midlands NHS Trust said it takes these incidents "extremely seriously".
Details of the error were published in papers of the joint meeting of North Staffordshire and Stoke-on-Trent Clinical Commissioning Groups on 2 October.
It said the guide wire was left in place after a central line insertion on 10 August.
The report said the wire was successfully removed and the patient suffered no ill-effects but added a "full investigation is being carried out".
The age and sex of the patient have not been revealed.
Since the incident, the report added UHNM is developing a local safety standard for invasive procedures.
A trust spokesman said: "UHNM has strict protocols to fully investigate any and all serious incidents that are recorded in our hospitals.
"Our staff work closely throughout the investigation period to understand why each incident occurs and how we can improve our practices."
CCG director of nursing and quality, Heather Johnstone, said: "This should never have happened and it is being investigated."