A health board is investigating a data breach that saw the personal details of 86 transgender patients at Glasgow's Sandyford Clinic accidentally revealed.
NHS Greater Glasgow and Clyde (GGC) said "human error" had led to patients' email addresses being included in an email that was sent out on Monday.
Some of the addresses also included name and date of birth information.
NHS GGC has informed the Information Commissioner and is contacting patients affected to "apologise unreservedly".
BBC Scotland understands that the patients involved attend the gender identity service at the Sandyford Clinic in Glasgow.
Their names were accidentally included in the "to" section of the email, rather than being concealed.
In a statement, NHS GGC said: "Yesterday 86 individuals were sent an e-mail with information on a forthcoming event.
"The member of staff sending this email made the unfortunate error of attaching all the email addresses of the patients in the one email.
"Patient confidentiality is of the highest priority and we are extremely concerned that this breach has occurred as a result of human error."
The statement added: "On review of the e-mail addresses we can confirm that a number of the individuals' names and dates of births are discernable from the email addresses.
"We have already made the Information Commissioner aware of this issue and have been guided by him."
Dr Pauline McGough, consultant in sexual and reproductive health at NHS GGC, said: "We are urgently taking the appropriate steps to contact the individuals concerned and will apologise unreservedly to them for any distress this may have caused.
"We will investigate this issue fully and take appropriate steps to ensure this does not happen again, including urgently reaffirming to staff the vital importance of handling sensitive data with the utmost diligence to maintain patient confidentiality."