The collision occurred on the B1257 Helmsley to Stokesley road near to the Laskill junction at around 2.30pm on Sunday 17 April 2011.
The motorcyclist, a 62-year-old man from Driffield, sustained serious injuries when his silver Honda CBR bike, which was travelling towards Helmsley from Stokesley, collided with a blue Kia Sorento, travelling in the opposite direction.
He remains in James Cook Hospital, in a poorly condition. The occupants of the Kia were uninjured.
Traffic Sergeant Clare Sawyer, of Thirsk Road Policing Group, said: “I am appealing for anyone who witnessed the collision to come forward with information.
“Anyone who saw the motorcycle, or the Kia, which was towing a caravan, prior to the incident may have information vital to the investigation.”
Anyone who can help the police with their enquiries is urged to contact TS Clare Sawyer, of Thirsk Road Policing Group, on 0845 60 60 24 7, quoting reference number NYP-17042011-0312.