An investigation has been launched into allegations that unauthorised people were allowed to watch procedures being carried out in hospital operating theatres.
Cardiff and Vale University Health Board said it was undertaking an internal review following the "deeply concerning" allegations.
An internal staff survey found that previous concerns regarding unauthorised people in theatres had been raised but not thoroughly investigated, the health board said.
"We want to reassure patients and their families that we are committed to providing safe and high-quality care, and patient safety and confidentiality is always of utmost importance to us," it said in a statement.