A 28-year-old man was seriously injured in a quad bike crash in Ellenbrook just after midnight on Saturday.
A police spokeswoman said a blue Yamaha quad bike was travelling on Farmaner Parkway towards Birkett Circle about 12.15am.
"At the T-intersection of Farmaner Parkway and Birkett Circle, the quad bike failed to negotiate the corner and lost control," the police spokeswoman said.
"The quad bike rolled several times before coming to a complete stop."
The Morley man received serious injuries and is in Royal Perth Hospital.
Police would like to speak to anyone who saw the crash or the quad bike prior to the crash.
Anyone with information is asked to call Crime Stoppers on 1800 333 000.