Some schools in Swansea may be closed as the city's council says almost £150m worth of repairs are needed.
£21.5m of work is needed at Bishop Gore Comprehensive in Sketty
The authority has spent the last two years assessing the state of school buildings and facilities.
It says tough choices are ahead with some needing new heating and lighting and others major structural repairs.
A meeting with head teachers, governors and others is due to take place next month although the council said it had no specific proposals at this stage.
Cabinet member for education Mike Day said a two year survey of city schools has produced a detailed breakdown of maintenance issues.
"We are being open and transparent in relation to the condition of our schools because we want to engage with stakeholders and we can only do this if people have the full picture."
The report reveals:
- 21 primary schools each need more than £1m worth of work.
- 12 secondary schools need the same including two of the city's oldest schools.
- Estimates suggest £21.5m is needed at Bishop Gore in Sketty and almost £17m at Bishop Vaughan.
"It is no surprise that, given the age of many of our schools, out-dated heating systems and leaking roofs and windows need replacing," added councillor Day.
"This is not a new issue and all councils in Wales face similar problems."
He said last winter some schools, including Cwmbwrla and Manselton Primary Schools closed for short periods while repairs were carried out.
"Safety is paramount and we would never put any child or staff member at risk.
"We regularly check our buildings and take all necessary precautions in the interests of the safety of pupils and teachers."
"But there's no quick fix. This is the result of a lack of investment in maintenance over a period of years."