A 16-year-old male suffered life threatening injuries in the crash.
Both teens are from Keswick.
York Regional police say the teens were in a van travelling southbound on McCowan Road when the driver lost control of the vehicle for an unknown reason.
The van veered into a ditch and hit a culvert. The teens were both ejected.
The accident happened at about 8:45 p.m.
No names have been released.