Britain's data watchdog said it was looking into a report that staff at the hospital where Kate, Princess of Wales, underwent abdominal surgery in January, had attempted to access her private health records.
The report in the Daily Mirror said managers at The London Clinic, where King Charles was also treated in January, were investigating claims that at least one member of staff had been caught trying to access Kate's medical notes.
A spokesperson for the Information Commissioner's Office said on Wednesday: "We can confirm that we have received a breach report and are assessing the information provided."
Kensington Palace said it was "a matter for The London Clinic".
Kate, 42, had surgery for a non-cancerous but unspecified condition during her stay of around two weeks in the hospital.
She stepped back from official duties and Kensington Palace has said she is not expected to return to royal engagements until after Easter.
Her absence from public life has triggered speculation, rumour and bizarre conspiracy theories about her health.
Kate's apology earlier this month for editing a photo taken by her husband William, the heir to the throne, to mark Mother's Day only sparked further intrigue.
On Monday, however, a video published by the Sun newspaper on its website showed her walking and carrying shopping bags alongside William at a farm shop in Windsor near their home.
Kensington Palace has not denied that the video is genuine, but has declined to comment on a matter it regards as being the royals' private time.
The London Clinic did not immediately respond to a request to comment.
