Some panels of combustible material have been found in cladding at Edinburgh Royal Infirmary, the Scottish government has said.
It emerged after a meeting of the working group set up to review building and fire safety in Scotland in the wake of the Grenfell Tower blaze in London.
The Scottish Fire and Rescue Service has carried out safety audits and confirmed the building is safe.
NHS Lothian is putting further safety measures in place, as a precaution.
These include controlling access to the building facade by introducing temporary fencing and increasing vigilance and security to prevent unauthorised people or vehicles from coming into contact with it.
Cladding made from an aluminium composite material is thought to have contributed to the rapid spread of the fire which engulfed Grenfell Tower in June.
Last month, NHS Greater Glasgow and Clyde said cladding similar to that used in the Grenfell Tower was to be removed from the Queen Elizabeth University Hospital building.
The Scottish government's working group on building and fire safety held its fifth meeting on Friday.
It was told that the University of Edinburgh had carried out out fire testing at the Royal Infirmary which indicated that "sections of panelling in the exterior facade contain some combustible material".
Health Secretary Shona Robison said: "We have received assurances from NHS Lothian and the Scottish Fire and Rescue Service that the Royal Infirmary of Edinburgh building remains safe.
"Patient safety remains our top priority, and I am reassured that the board is putting in place immediate, precautionary measures while further investigations take place."
NHS Lothian chief executive Tim Davison said: "We take all matters surrounding fire safety very seriously and I would like to reassure patients, the public and our staff that the Royal Infirmary of Edinburgh has a sophisticated fire prevention system.
"Our risk assessments and the additional measures we have put in place give us confidence that the hospital remains safe for our patients and staff. This confidence is endorsed by Scottish Fire and Rescue."
Since June, NHS Lothian has been undertaking a review of all its buildings' external cladding, including risk assessments and necessary testing.
A second phase of testing of the cladding at Edinburgh Royal Infirmary, in line with British Standard 8414, will be carried out, with the timeframe estimated at six weeks.
At the government's working group meeting, ministers also welcomed the launch of a consultation on fire and building safety aimed at better protecting all homes against fire and smoke.
It will look at whether the same standard should be applied across all housing - whether it is new-build, privately or socially rented or owner-occupied.
Communities Secretary Angela Constance added: "We remain confident that we have stringent building and fire safety regulations in Scotland, and through this group we will ensure that we will continue to have the highest standards in place.
"I'd like to thank local authorities, fire and rescue and health services, housing associations and building owners for their continued efforts.
"We are working closely together through this review of our regulations and will take any action that is needed."