The Brighton Hippodrome, the Grade II* listed theatre, is among the 48 venues that are at real risk of being demolished or are in critical physical condition.
The Theatre Buildings at Risk Register this year has added 10 new at risk buildings and revealed that four have been lost forever.
As well as the listed Brighton venue which has not been protected by its heritage status, the Derby Hippodrome, the Theatre Royal Hyde and Swansea Palace are among those that have been given the highest at risk assessment.
Mhora Samuel, director of The Theatres Trust said, "We are at risk of losing really important and historic theatre buildings as a result of neglect, development and demolition. It's so sad to see theatres treated this way."
Others include the Alexandra Palace Theatre, Hulme Hippodrome, the Dudley Hippodrome and the Futurist in Scarborough.
Among the new additions to the list are the Coronet in Elephant and Castle, London, and the former Theatre Royal in Manchester which are on sites earmarked for redevelopment.
Some theatres have been left to rot, destroyed by water damage and Buddleia, while others face being torn down by developers.
The venues lost forever are St Peters Theatre Southsea, the Cochrane Theatre and the Mermaid Theatre in London. This came after the local authorities determined they would no longer be classed as theatres and the sites will be redeveloped. The Precinct Theatre in Islington has also gone for redevelopment.