Police believe a Harvey man was not wearing a seatbelt when he was thrown from his vehicle in the South West.
The 45-year-old man was driving along the South Western Highway around 6.25pm on Thursday when he lost control of his vehicle near Mornington Road in Wokalup.
The vehicle collided with a sign and rolled.
The driver sustained serious head injuries after being thrown from the rolling car.
He was airlifted to Royal Perth Hospital by the rescue helicopter.
The 19-year-old male passenger from Harvey sustained minor injuries.