The smash happened on New Rowley Road, at the junction with Banklands Road, just before 7.30pm yesterday.
The male rider was taken to Queen Elizabeth Hospital in Birmingham where he is being treated for multiple leg fractures, police said.
Jamie Arrowsmith, spokesman for West Midlands Ambulance Service, said: "We were called to reports of a collision between a car and a motorbike on New Rowley Road at 7.26pm last night.
"One ambulance, a paramedic officer and the MERIT team, including a doctor and a critical care paramedic attended the scene.
"On arrival we discovered one patient, a teenage male, who was the motorcyclist.
"He was treated for a serious injury at the scene before being taken to Queen Elizabeth Hospital for further treatment."
A West Midlands Police spokesman said: "We were alerted to a serious road collision at around 7.30pm last night at the junction of New Rowley Road and Banklands Road in Dudley.
"A teenager riding an off-road bike suffered serious leg injuries after colliding with a car.
"He is in hospital with multiple leg fractures; his condition is potentially life-changing.
"The driver of the car was not seriously hurt. Any witnesses are urged to message us via Live Chat on our website or by calling 101; please quote log 4132 from 15 October."