The crash happened shortly after 8.30pm when a Yamaha CBR 125 bike collided with a pedestrian on the A6038 Otley Road in Baildon, West Yorkshire.
The rider, an 18-year-old man, fell from his bike and was taken to Leeds General Infirmary with life-threatening injuries and died yesterday (Sunday).
The pedestrian, a 60-year-old man, was also seriously injured, but has now been discharged from hospital after treatment.
Sergeant Carl Quinn of the Major Collision and Enquiry Team, said: “We are carrying out a number of enquiries into this fatal collision and I am keen to speak with anyone who saw what took place.
“I would also like to speak with anyone or who may have seen either the pedestrian or motorbike on Otley Road just prior to the incident.
“Anyone who saw what happened or who has dashcam footage is asked to contact the Major Collision and Enquiry Team on 101.”