The crash involved a motorcycle and a car on the westbound A69 Haltwistle Bypass at the junction with Bellister Bank at 5.45pm on Saturday (October 8).
The Yamaha motorcycle was turning right into the eastbound carriageway when it collided with a Renault Clio, which was travelling westbound.
The 22-year-old woman motorcycle rider suffered serious injuries and was taken by air ambulance to the RVI, where her condition is described as stable. The car driver, a 45-year-old woman, suffered minor injuries.
The A69 was closed in both directions either side of Haltwhistle while the casualties were dealt with and the scene was examined by officers.
Police are now appealing for witnesses. Anyone who was in the area at the time and who may have witnesses the incident is asked to call Northumbria Police on 101, quoting reference number 962 08/10/16.