Authorities are investigating the death of a 20-year-old Aboriginal man at Western Australia's Casuarina Prison.
WA's Department of Corrective Services confirmed the man had been found at around 3.50pm (WST) on Wednesday afternoon.
Efforts to revive him were unsuccessful.
A coronial inquiry has been launched into the death in custody, and WA police are conducting an investigation.
The man's next of kin have been notified.