A sick child was turned away from hospital because of concerns about dust and debris in the operating theatre.
A surgeon cancelled the operation after turning up at the Royal Alexandra Hospital for Sick Children in Brighton and finding an important screen had been removed.
Essential work is being carried out on the main operating theatre at the hospital in Dyke Road, Brighton, but the second theatre has remained open.
A screen had blocked access to the main theatre to ensure no dust or debris could get in.
Positive pressure ventilation was also used to keep the second theatre clean.
However, contractors had to remove the screen temporarily on Thursday to transfer equipment.
A spokeswoman for the Brighton and Sussex University Hospitals NHS Trust, which runs the hospital, said this was rare and the builders had done everything possible to minimise disruption.
She said: "A surgeon due to carry out an operation arrived and made a clinical decision that, since the operation he was due to perform was invasive, he would postpone the procedure.
"He felt although all reasonable efforts had been made to keep the theatre clean, it was best not to take any chances.
"No other operations have had to be cancelled."
A letter was being sent to the girls' parents, offering them a new booking on September 18.
The girl's father, who did not want to be named, said: "We were told right at the last minute that the operation couldn't go ahead.
"My daughter was quite distressed."
The main theatre has been closed since July 21 for essential decontamination work.
It was due to finish today and both theatres are expected to be fully functional from September 8.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article