NHS Highland has launched a probe after a patient was mistakenly sent medical information relating to someone else.
Peter Todd was shocked to find it among his file, which he had sought as he continues his recovery from a mental health condition.
The file, which he received through the post on Wednesday, also contained confidential material about a clinician.
The 39-year-old from Caithness has since returned the file and received an apology from an official of the health board.
Mr Todd has been assured the “rogue” information will be securely destroyed.
He said: “It’s a blatant breach of confidentiality.
“I was completely astonished when I saw the personal and medical history of the other individual within my file.
“There was also personal information about a clinician.
“That, to me, is totally inexcusable.”
Concerns NHS Highland may have mixed up files
Mr Todd, from Thurso, is concerned that some of his medical information may have ended up on the other patient’s file.
He met on Thursday with NHS Highland Caithness district manager Christian Nicolson who arranged to have the outside material deleted from the file.
Mr Todd said: “She and (chief executive) Pam Dudek have accepted that what happened was unacceptable and they have launched an immediate investigation.
“I’d certainly praise them for taking swift action to sort out this fiasco.”
A NHS Highland spokesman said: “NHS Highland apologise that an administrative error has led to a document being shared with another member of the public which contains limited personal data.
“We have informed the Information Commissioner Office and are seeking to make contact with the individual concerned to give our apologies directly.”