Surgery carried out on the wrong part of the body went undetected for five years in one of three "never events" at a hospital.
A "wrong-sided prosthesis" was fitted in a separate event and a swab was left in a patient on another occasion.
The events at Derriford Hospital in Plymouth were revealed in board papers ahead of a meeting on Friday.
The hospital has apologised and said "comprehensive investigations" were being carried out.
The "wrong site" surgery was carried out in 2010 but was not discovered until March 2015, the same month as the "retained swab" incident.
'Occasionally mistakes happen'
A hospital spokesman said the discovery of a "wrong-sided prosthesis" in April 2015 could refer to a joint such as a knee, shoulder or hip.
Ann James, chief executive of Plymouth Hospitals NHS Trust, said: "We have apologised personally to the patients affected and we are extremely sorry that these mistakes have happened."
The trust said it treated half a million patients every year.
"But as our staff are human, very occasionally mistakes happen and things do not go as planned," said Mrs James.
A spokesman for the trust declined to elaborate on any details regarding the incidents "for reasons of patient confidentiality".
Derriford Hospital went on 'black alert' in January and February when it was unable to cope with the number of patients coming in.
The Care Quality Commission investigated Derriford in 2013 after eight never events within a year.