The boy, who was travelling in the front passenger seat, is being treated for serious head injuries at Queen Elizabeth University Hospital, Glasgow.
Three other teenagers were also taken to hospital after the crash in Glasgow on Saturday afternoon.
The Ford Fiesta they were travelling in left the road and hit a tree between Easterhouse and Gartcosh.
The driver of the car, also 17, was taken to Monklands District General Hospital, where his condition was stable.
A 19-year-old was being treated for foot injuries at Glasgow Royal Infirmary, while a 16-year-old boy was treated for minor injuries at Wishaw General Hospital.
Police Scotland constable Gordon Bremner said: “I am keen to hear from anyone who may have seen the car prior to the crash.”