Safety netting has been erected around the Queen Elizabeth University Hospital in Glasgow after a glass panel fell from the 10th floor.
NHS Greater Glasgow and Clyde (NHSGGC) said an investigation into the incident earlier this month proved inconclusive.
It is understood panels have fallen from the £842m building on at least three occasions since it opened.
In the latest incident the panel shattered near the front entrance but no-one was injured.
An NHSGGC spokeswoman said: "It has not been possible to establish the cause of this decorative external glass panel shattering before falling to the ground on 9 August.
"The shattered pieces recovered were not large enough to analyse and determine the cause.
"However, the safety of our patients, visitors and staff is our paramount priority which is why we have installed safety netting where these panels are situated on the building."
The QEUH opened in April 2015 and featured in the BBC series Scotland's Superhospital.