Dyfed-Powys Police is investigating a three-vehicle collision which happened at around 2.10pm on Wednesday, October 4.
The collision took place between Presteigne and Combe on the B4362.
A blue Suzuki motorbike, a silver Ford Transit van and a white Renault Megan were involved.
The motorbike rider sustained serious injuries.
"Anyone with information that could help officers with their investigation or anyone who was travelling along the road at the relevant time with dashcam footage is asked to report it to Dyfed-Powys Police."
If you are deaf, hard of hearing, or speech impaired text the non-emergency number on 07811 311 908
Quote reference: 23000965473