The Royal Cornwall Hospital has suspended members of staff and closed a medical ward as part of an investigation into a patient's care.
The hospital said "a couple" of staff working on the 24-bed Wheal Agar ward, which deals mainly with elderly patients, had been suspended as a "neutral act" while it investigated allegations about the care of a single patient.
The ward at the hospital in Truro closed at the weekend after the complaint was made last week.
A hospital spokesman said: "As a matter of routine, we take every concern raised seriously and, accordingly in this instance, we are exploring the matter fully.
"We can confirm staff have been suspended – this is a neutral act.
"The ward has been temporarily closed and any new patients will continue to be able to receive care and treatment within our hospital's services."
Details of the complaint, which is being investigated by senior hospital managers, have not been revealed.
Graham Webster, vice-chairman of campaign group Health Initiative Cornwall, said: "We do support any action being taken by the trust in regards to improving patient care, but we are extremely concerned that a vital ward is not open at this hospital which therefore effects its capability to deal with patients at this time of year."