The 17-year-old boy was driving a Piaggio Zip moped which collided with a Peugeot 208 car in the town yesterday afternoon.
West Yorkshire Police today issued an appeal for witnesses to the crash at the junction of the A643 Hardwick Road and Water Lane at just before 2.30pm.
Both vehicles were driving in the direction of Ackworth when the collision happened.
A spokesman said the moped driver suffered serious injuries and was taken to Leeds General Infirmary, where is in a stable condition.
Anyone who witnessed the collision is asked to contact PC Andy Wilson at Safer Roads East via 101.