Gauze was left in a patient's body after a throat operation earlier this month - one of a growing list of recent medical blunders at public hospitals.
The case was one of three disclosed yesterday, with the hospitals scrambling to explain how the mistakes had happened. The revelations added to the embarrassment of the Hospital Authority.
In the incident with the gauze, the patient was being treated for cancer and underwent an operation to remove his larynx and pharynx on July 5 in United Christian Hospital.
Doctors were unaware of the gauze until X-rays were taken on Thursday.
They explained the situation to the patient and his relatives and apologised. An investigation is under way to see whether improvements can be made.
The second blunder involved the injection of 10 times the dosage of an antidote to a patient undergoing surgery in July last year at Queen Elizabeth Hospital.