The woman was admitted to Dumfries and Galloway Royal Infirmary for a pelvic floor repair procedure.
A report by the Scottish Public Services Ombudsman said the woman had a vaginal hysterectomy later that day.
The ombudsman said the woman, known as Mrs C, should have been told about the possibility of the procedure earlier.
The report added: "We found that it was unreasonable that Mrs C was only told about the possibility of such a significant procedure on the day of the surgery and that she was given little time to consider this."
The ombudsman recommended that NHS Dumfries and Galloway issue a written apology to the patient.
It also asked the health board to provide evidence to show that the possibility of a hysterectomy is discussed at an early stage with patients undergoing pelvic floor repair.
A spokeswoman for the board said: "Jeff Ace, chief executive NHS Dumfries and Galloway, has written and apologised to this lady for her experience as it was not the standard that he would wish.
"The action plan for the actions requested by the SPSO has also been completed to ensure that we maximise the learning from her experience."
An NHS board has apologised to a patient who was told she may need a hysterectomy just hours before undergoing surgery for another matter.