Britain's only Grade I listed pier is top of the buildings on a risk list issued by English Heritage.
The West Pier in Brighton is described as being "in very bad condition" by the conservation group.
The pier, built in 1866, is, however, in line for a National Lottery grant and has private sector partners prepared to rescue it.
The group's register contains the most important buildings in the UK to be threatened by neglect and decay.
It also includes Hastings Castle, the manor house at Ore and the Dome cinema in Worthing. Other buildings in Brighton, include Marlborough House and Martello Court, the Thirties-style flats on the sea-front.
Also mentioned are Newhaven Fort, the ruins of Lewes Priory and the toll bridge over the River Adur at Shoreham.
Launching the register, English Heritage chairman, Sir Neil Cossons, said councils should compile their own list of Grade II buildings at risk. The national survey covers only Grade I and Grade II* buildings.
He said: "Last year, English Heritage offered £5.7 million of grant aid towards 98 buildings on the register. But to save all the entries could cost £400 million, far more than we can afford.
"I urge the Government to recognise the enormous regeneration potential such an investment would achieve."
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