Sussex Police said a 15-year-old boy suffered a serious head injury when he fell two storeys from a car park at Brighton Marina.
Emergency services were called to the scene at 5.45pm on Tuesday (March 28).
Police said the teenager was taken by air ambulance to St George’s Hospital in South London to be treated for a serious head injury.
A police spokesman said: “No update has been received on his condition since then. The incident is not being treated as suspicious.”