Two cars collided head on and a third swerved to avoid the crash and overturned by the side of the B769 near Stewarton, East Ayrshire, at around 6.35pm last night.
Two 18-year-old men were travelling southbound in a Vauxhall Corsa when they collided with a northbound Peugeot 206 carrying a 64-year-old male driver and his 52-year-old female passenger.
The woman died at the scene while the Peugeot driver was taken to Crosshouse Hospital in Kilmarnock, where his condition is described as stable.
The passenger in the Corsa is in a critical condition at Crosshouse with head and shoulder injuries, while the driver is in a stable condition with shoulder and arm injuries.
A third 18-year-old man was driving a Fiat 500 behind the Corsa. He swerved to avoid the crash and overturned. He escaped with an arm injury and was released from Crosshouse shortly after treatment.
Police are appealing for witnesses and a report will be sent to the procurator fiscal.