The move into a new £150m children's hospital in Edinburgh will be delayed until May 2018.
The new Royal Hospital for Sick Children in Edinburgh was originally due to open in autumn 2017.
The date was then pushed back to February 2018.
Now officials have confirmed it will be after Easter before they begin moving all 14 departments from Sciennes over to the new building at Little France on the outskirts of the capital.
An NHS Lothian spokeswoman said: "We are revising our internal staff moving dates to ensure that all services move in a safe and effective manner.
"We anticipate the Royal Hospital for Children and Young People, Department for Clinical Neurosciences and Child & Adolescents Mental Health Services will open to patients in spring 2018.
"However, until we have the revised migration timetable agreed these dates cannot be confirmed.
"This is a huge project and it's vital that the building is fully operational before it opens to ensure we provide the best possible care to all our patients.
"Staff are being kept up-to-date with any developments on moving dates."
A Scottish government spokesman said: "NHS Lothian have made us aware of the situation and we are continuing to liaise with them to ensure everything possible is being done to ensure the new hospital opens as soon as possible."