Police have launched an investigation into the cause of the accident, which happened at around 6.35pm on Sunday the B769 near Stewarton.
An 18-year-old driver of a Vauxhall Corsa was travelling northbound on the carriageway when his car collided with a Peugeot 206, travelling in the opposite direction.
Another vehicle, a Fiat 500, was overturned as it swerved off the road to avoid the crash.
A 52-year-old female passenger in the Peugeot died at the scene and the car's 64-year-old driver was taken to Crosshouse Hospital but is in a stable condition.
An 18-year-old passenger of the Corsa was also rushed to Crosshouse hospital by emergency crews, and is being treated for head and abdominal injuries.
Hospital staff have described his condition as critical.
The 18-year-old driver of the Vauxhall Corsa was taken to Crosshouse Hospital where he is being treated for shoulder and arm injuries. Hospital staff describe his condition as stable.
The 18-year-old driver of the Fiat was taken to Crosshouse Hospital and released after treatment for an arm injury.