City workers join celebrities including DJ Sara Cox and singer Rebecca Ferguson to bed down for the night in Exchange Square near Liverpool Street tonight.
The temporary rough sleepers will be treated to live music, ice skating performances and a bedtime story read to from Christopher Biggins.
Hundreds of people across London are expected to swap their beds for a sleeping bag tonight.
Every year, Centrepoint, which supports and campaigns for homeless young people aged 16-25 years, holds its Sleep Out event, encouraging people, businesses and celebrities, to take to the street.
It's the ninth year the charity has held the event and aims to raise £750,000 for homeless young people, to help house and support them over the Christmas period.
The number of young people sleeping rough in London has more than doubled over the last year. Homelessness charity Centrepoint says there are now more than 600 under-25s sleeping out on the capital's streets and they fear that rising youth unemployment could make things worse.
Sharon Thomas reports.