Police said a 56-year-old man from West Sussex was arrested on suspicion of dangerous driving following an accident on the A26 at Ringmer, between Lewes and Uckfield, on Friday afternoon.
Emergency services attended the scene at around 2pm near the Cock Inn where a silver car and black Suzuki Ignis, driven by a man from Kent, were involved in a head on collision.
The driver of the Suzuki Ignis, was taken to the Royal Sussex County Hospital.
The road was closed between Ham Lane and Earwig Corner while police investigated the crash.
A police helicopter and Kent Air Ambulance are pictured at the scene of the crash.