Fewer than half of the buildings owned by Leeds hospitals are occupied by patients.
The city's hospitals trust has the biggest estate in the NHS but just 40 per cent of it is designated for patient occupation.
Trust chiefs say most buildings – apart from the newest – are 'less than acceptable' and in need of major investment soon.
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Some operating theatres in use at Leeds General Infirmary were opened in 1915.
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A backlog of building work has reduced, but still stands at 134m.
Hospital bosses have drawn up a masterplan to cut the size of the estate by 25 per cent over the next 10 years.
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Darryn Kerr, director of estates and facilities, said: "The historic nature of parts of the estate and ad-hoc development over many years means some areas now fail to meet requirements of modern and progressive healthcare."
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Leeds Teaching Hospitals NHS Trust runs five hospitals on land totalling 50.4 hectares – the largest estate in the NHS in England.
Running costs stand at 92.5m a year and buildings are valued at 571m, with land at 70m.
The new blueprint for the future shows the scale of the task of bringing the below-par buildings up to scratch:
* Leeds General Infirmary where 70 per cent of the buildings are more than 25 years old and 25 per cent of the site dates from before the formation of the NHS in 1948. Listed buildings include the Gilbert Scott Building and the Old Medical School;
* At St James's Hospital 47 per cent of buildings are more than 25 years old. Parts of the site are listed, including the chapel, pathology lab and Thackray Medical Museum. It also has the largest building work backlog of 66m;
* Seacroft Hospital's clock tower and administration block are listed and several blocks are empty and patient services are now concentrated in one area of the large site;
* Chapel Allerton Hospital has the highest proportion of buildings in a high risk condition at five per cent.
Hospital chiefs say they need to see more patients and become more efficient so the size of the estate must be cut by a quarter.
Mr Kerr's report said: "Some buildings are of a very high quality and some of the poorest accommodation has been vacated, however many parts of the estate have poor functionality and reflect many years of limited investment in maintenance."
It added that work is already under way to move out of some poor quality accommodation and over the coming years the plan is to vacate even more.