A broken blade and part of a drill are among items which have been left inside Tayside patients by blundering medics over the last four years.
Data released under the Freedom of Information Act has revealed that nine items were left behind following surgery at NHS Tayside hospitals.
Other objects accidently left inside patients include swabs and a piece of a contraceptive device.
Most of the forgotten items were discovered during surgery while others were found following CT scans, ultrasounds and X-rays.
The incidents took place at Ninewells Hospital, Perth Royal Infirmary and Drumhar Community Hospital.
The health board said one patient became unwell as a result but made a full recovery.
Margaret Watt, chairwoman of the Scotland Patients Association, described the errors as “completely unacceptable”.
She said: “These kind of mishaps have been going on for too long I can only imagine how horrible an experience that would be for a patient.
“The last thing you would want is to have surgery again because someone has left something inside you and we don’t know how much damage it could cause to your body.”
General surgery protocol includes counting the items to be used during procedures, including each individual cotton swab.
Ms Watt added: “Staff are supposed to check the number of instruments when you go into theatre and when you are finished to make sure they have got everything.
“A shortage of staff has an impact and mistakes can happen but these types of mistakes should not happen at all.”
It is understood that at least one patient is currently taking legal action against the health board as a result of their experience.
An NHS Tayside spokeswoman said: “When a foreign body is unknowingly left within a patient, this is a failure of our safety system.
“We recognise the importance of avoiding these events and have systems in place to manage the significant amount of equipment and consumables used on a daily basis within the surgical environment.
“We formally review each occurrence of a retained item to ensure appropriate processes were followed and make any necessary improvements which are then shared with the wider clinical team across Tayside.”