The crash happened at about 9.30pm, near Swindon Lane, Harewood, on the A61, yesterday (Thursday).
A blue and white-coloured motorcycle was involved in a collision with a white articulated lorry.
The motorcycle rider, a 21-year-old man from Leeds, suffered serious head and chest injuries during the crash.
He was taken to Leeds General Infirmary, where police said he is now receiving treatment.
The 47-year-old lorry driver, from Leeds, was uninjured but shaken. He is assisting officers with the investigation.
Diversions were put in place following the crash.
Anyone with information about the collision is asked to call police on 101, quoting reference number 12180067106.